Implemented nullable reference types support

Examples/01-PublishSubscribe/01-PublishSubscribe.csproj

@@ -4,6 +4,7 @@
     <OutputType>Exe</OutputType>
     <TargetFramework>net6.0</TargetFramework>
     <RootNamespace>_01_PublishSubscribe</RootNamespace>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

Examples/02-DeclareDurableQueues/02-DeclareDurableQueues.csproj

@@ -4,6 +4,7 @@
     <OutputType>Exe</OutputType>
     <TargetFramework>net6.0</TargetFramework>
     <RootNamespace>_02_DeclareDurableQueues</RootNamespace>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

Examples/03-FlowRequestResponse/03-FlowRequestResponse.csproj

@@ -4,6 +4,7 @@
     <OutputType>Exe</OutputType>
     <TargetFramework>net6.0</TargetFramework>
     <RootNamespace>_03_FlowRequestResponse</RootNamespace>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

Examples/03-FlowRequestResponse/ParallelFlowController.cs

@@ -15,9 +15,9 @@ namespace _03_FlowRequestResponse
         private readonly IFlowProvider flowProvider;
         private readonly IExampleState exampleState;
 
-        public string FirstQuote;
+        public string? FirstQuote;
-        public string SecondQuote;
+        public string? SecondQuote;
-        public string ThirdQuote;
+        public string? ThirdQuote;
 
 
         public ParallelFlowController(IFlowProvider flowProvider, IExampleState exampleState)

Examples/04-Transient/04-Transient.csproj

@@ -4,6 +4,7 @@
     <OutputType>Exe</OutputType>
     <TargetFramework>net6.0</TargetFramework>
     <RootNamespace>_04_Transient</RootNamespace>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

Examples/05-SpeedTest/05-SpeedTest.csproj

@@ -4,6 +4,7 @@
     <OutputType>Exe</OutputType>
     <TargetFramework>net6.0</TargetFramework>
     <RootNamespace>_05_SpeedTest</RootNamespace>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

Examples/06-StatelessRequestResponse/06-StatelessRequestResponse.csproj

@@ -4,6 +4,7 @@
     <OutputType>Exe</OutputType>
     <TargetFramework>net6.0</TargetFramework>
     <RootNamespace>_06_StatelessRequestResponse</RootNamespace>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

Examples/07-ParallelizationTest/07-ParallelizationTest.csproj

@@ -4,6 +4,7 @@
     <OutputType>Exe</OutputType>
     <TargetFramework>net6.0</TargetFramework>
     <RootNamespace>_07_ParallelizationTest</RootNamespace>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

Examples/07-ParallelizationTest/Program.cs

@@ -107,7 +107,7 @@ namespace _07_ParallelizationTest
         private int count;
         private readonly object waitLock = new();
         private TaskCompletionSource<bool> batchReachedTask = new();
-        private Timer messageExpectedTimer;
+        private Timer? messageExpectedTimer;
         private readonly TimeSpan messageExpectedTimeout = TimeSpan.FromMilliseconds(5000);
 
 

Examples/08-MessageHandlerLogging/08-MessageHandlerLogging.csproj

@@ -4,6 +4,7 @@
     <OutputType>Exe</OutputType>
     <TargetFramework>net6.0</TargetFramework>
     <RootNamespace>_08_MessageHandlerLogging</RootNamespace>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

Examples/ExampleLib/ExampleLib.csproj

@@ -3,6 +3,7 @@
   <PropertyGroup>
     <TargetFramework>net6.0</TargetFramework>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

Tapeti.Autofac/AutofacDependencyResolver.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using Autofac;
 using Autofac.Builder;
 
@@ -14,21 +15,20 @@ namespace Tapeti.Autofac
     /// </summary>
     public class AutofacDependencyResolver : IDependencyContainer
     {
-        private ContainerBuilder containerBuilder;
+        private ContainerBuilder? containerBuilder;
-        private IContainer container;
+        private IContainer? container;
 
 
         /// <summary>
-        /// The built container. Either set directly, or use the Build method to built the
+        /// The built container. Either set directly, or use the Build method to build the
         /// update this reference.
         /// </summary>
         public IContainer Container
         {
-            get => container;
+            get => container ?? throw new ArgumentNullException(nameof(container));
             set
             {
                 container = value;
-                if (value != null)
                 containerBuilder = null;
             }
         }
@@ -50,7 +50,7 @@ namespace Tapeti.Autofac
             CheckContainerBuilder();
             Container = containerBuilder.Build(options);
 
-            return container;
+            return Container;
         }
 
 
@@ -141,6 +141,7 @@ namespace Tapeti.Autofac
         }
 
 
+        [MemberNotNull(nameof(containerBuilder))]
         private void CheckContainerBuilder()
         {
             if (containerBuilder == null)

Tapeti.Autofac/Tapeti.Autofac.csproj

@@ -12,6 +12,7 @@
     <PackageIcon>Tapeti.SimpleInjector.png</PackageIcon>
     <Version>2.0.0</Version>
     <LangVersion>9</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

Tapeti.CastleWindsor/Tapeti.CastleWindsor.csproj

@@ -12,6 +12,7 @@
     <PackageIcon>Tapeti.SimpleInjector.png</PackageIcon>
     <Version>2.0.0</Version>
     <LangVersion>9</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

Tapeti.DataAnnotations/DataAnnotationsMessageMiddleware.cs

@@ -13,6 +13,9 @@ namespace Tapeti.DataAnnotations
         /// <inheritdoc />
         public ValueTask Handle(IMessageContext context, Func<ValueTask> next)
         {
+            if (context.Message == null) 
+                return next();
+
             var validationContext = new ValidationContext(context.Message);
             Validator.ValidateObject(context.Message, validationContext, true);
 

Tapeti.DataAnnotations/Tapeti.DataAnnotations.csproj

@@ -12,6 +12,7 @@
     <PackageIcon>Tapeti.DataAnnotations.png</PackageIcon>
     <Version>2.0.0</Version>
     <LangVersion>9</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">

Tapeti.Flow.SQL/ConfigExtensions.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Linq;
 using Tapeti.Config;
 
 // ReSharper disable UnusedMember.Global
@@ -45,7 +46,7 @@ namespace Tapeti.Flow.SQL
 
         public IEnumerable<object> GetMiddleware(IDependencyResolver dependencyResolver)
         {
-            return null;
+            return Enumerable.Empty<object>();
         }
     }
 }

Tapeti.Flow.SQL/SqlConnectionFlowRepository.cs

@@ -58,6 +58,7 @@ namespace Tapeti.Flow.SQL
                         var stateJson = flowReader.GetString(2);
 
                         var state = JsonConvert.DeserializeObject<T>(stateJson);
+                        if (state != null)
                             result.Add(new FlowRecord<T>(flowID, creationTime, state));
                     }
 

Tapeti.Flow.SQL/SqlExceptionHelper.cs

@@ -38,11 +38,13 @@ namespace Tapeti.Flow.SQL
         /// <summary>
         /// Extracts alls SqlExceptions from the main and inner or aggregate exceptions
         /// </summary>
-        public static IEnumerable<SqlException> ExtractSqlExceptions(Exception e)
+        public static IEnumerable<SqlException> ExtractSqlExceptions(Exception exception)
         {
-            while (e != null)
+            var exceptionHead = exception;
+
+            while (exceptionHead != null)
             {
-                switch (e)
+                switch (exceptionHead)
                 {
                     case AggregateException aggregateException:
                         foreach (var innerException in aggregateException.InnerExceptions)
@@ -56,7 +58,8 @@ namespace Tapeti.Flow.SQL
                         yield return sqlException;
                         break;
                 }
-                e = e.InnerException;
+
+                exceptionHead = exceptionHead.InnerException;
             }
         }
 
@@ -66,12 +69,14 @@ namespace Tapeti.Flow.SQL
         /// </summary>
         public static IEnumerable<SqlError> UnwrapSqlErrors(SqlException exception)
         {
-            while (exception != null)
+            var exceptionHead = exception;
+
+            while (exceptionHead != null)
             {
-                foreach (SqlError error in exception.Errors)
+                foreach (SqlError error in exceptionHead.Errors)
                     yield return error;
 
-                exception = exception.InnerException as SqlException;
+                exceptionHead = exceptionHead.InnerException as SqlException;
             }
         }
 

Tapeti.Flow.SQL/SqlRetryHelper.cs

@@ -54,7 +54,7 @@ namespace Tapeti.Flow.SQL
                 returnValue = await callback();
             });
 
-            return returnValue;
+            return returnValue!;
         }
     }
 }

Tapeti.Flow.SQL/Tapeti.Flow.SQL.csproj

@@ -12,6 +12,7 @@
     <PackageIcon>Tapeti.Flow.SQL.png</PackageIcon>
     <Version>2.0.0</Version>
     <LangVersion>9</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">

Tapeti.Flow/ConfigExtensions.cs

@@ -15,7 +15,7 @@ namespace Tapeti.Flow
         /// <param name="config"></param>
         /// <param name="flowRepository">An optional IFlowRepository implementation to persist flow state. If not provided, flow state will be lost when the application restarts.</param>
         /// <returns></returns>
-        public static ITapetiConfigBuilder WithFlow(this ITapetiConfigBuilder config, IFlowRepository flowRepository = null)
+        public static ITapetiConfigBuilder WithFlow(this ITapetiConfigBuilder config, IFlowRepository? flowRepository = null)
         {
             config.Use(new FlowExtension(flowRepository));
             return config;

Tapeti.Flow/Default/FlowBindingMiddleware.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics;
 using System.Linq;
 using System.Reflection;
 using System.Threading.Tasks;
@@ -46,6 +47,9 @@ namespace Tapeti.Flow.Default
             {
                 context.Result.SetHandler(async (messageContext, value) =>
                 {
+                    if (value == null)
+                        throw new InvalidOperationException("Return value should be a Task, not null");
+
                     await (Task)value;
                     await HandleParallelResponse(messageContext);
                 });
@@ -54,6 +58,10 @@ namespace Tapeti.Flow.Default
             {
                 context.Result.SetHandler(async (messageContext, value) =>
                 {
+                    if (value == null)
+                        // ValueTask is a struct and should never be null
+                        throw new UnreachableException("Return value should be a ValueTask, not null");
+
                     await (ValueTask)value;
                     await HandleParallelResponse(messageContext);
                 });
@@ -82,14 +90,22 @@ namespace Tapeti.Flow.Default
             switch (taskType)
             {
                 case TaskType.None:
-                    context.Result.SetHandler((messageContext, value) => HandleYieldPoint(messageContext, (IYieldPoint)value));
+                    context.Result.SetHandler((messageContext, value) =>
+                    {
+                        if (value == null)
+                            throw new InvalidOperationException("Return value should be an IYieldPoint, not null");
+
+                        return HandleYieldPoint(messageContext, (IYieldPoint)value);
+                    });
                     break;
 
                 case TaskType.Task:
                     context.Result.SetHandler(async (messageContext, value) =>
                     {
+                        if (value == null)
+                            throw new InvalidOperationException("Return value should be a Task<IYieldPoint>, not null");
+
                         var yieldPoint = await (Task<IYieldPoint>)value;
-                        if (yieldPoint != null)
                         await HandleYieldPoint(messageContext, yieldPoint);
                     });
                     break;
@@ -97,8 +113,11 @@ namespace Tapeti.Flow.Default
                 case TaskType.ValueTask:
                     context.Result.SetHandler(async (messageContext, value) =>
                     {
+                        if (value == null)
+                            // ValueTask is a struct and should never be null
+                            throw new UnreachableException("Return value should be a ValueTask<IYieldPoint>, not null");
+
                         var yieldPoint = await (ValueTask<IYieldPoint>)value;
-                        if (yieldPoint != null)
                         await HandleYieldPoint(messageContext, yieldPoint);
                     });
                     break;
@@ -140,7 +159,7 @@ namespace Tapeti.Flow.Default
         }
 
 
-        private static object ParallelRequestParameterFactory(IMessageContext context)
+        private static object? ParallelRequestParameterFactory(IMessageContext context)
         {
             var flowHandler = context.Config.DependencyResolver.Resolve<IFlowHandler>();
             return flowHandler.GetParallelRequest(new FlowHandlerContext(context));

Tapeti.Flow/Default/FlowContext.cs

@@ -6,25 +6,49 @@ namespace Tapeti.Flow.Default
 {
     internal class FlowContext : IDisposable
     {
-        public IFlowHandlerContext HandlerContext { get; set; }
+        private readonly IFlowHandlerContext? handlerContext;
-        public IFlowStateLock FlowStateLock { get; set; }
+        private IFlowStateLock? flowStateLock;
-        public FlowState FlowState { get; set; }
+        private FlowState? flowState;
+
+
+        public IFlowHandlerContext HandlerContext => handlerContext ?? throw new InvalidOperationException("FlowContext does not have a HandlerContext");
+        public IFlowStateLock FlowStateLock => flowStateLock ?? throw new InvalidOperationException("FlowContext does not have a FlowStateLock");
+        public FlowState FlowState => flowState ?? throw new InvalidOperationException("FlowContext does not have a FlowState");
+
+        public bool HasFlowStateAndLock => flowState != null && flowStateLock != null;
 
         public Guid ContinuationID { get; set; }
-        public ContinuationMetadata ContinuationMetadata { get; set; }
+        public ContinuationMetadata? ContinuationMetadata { get; set; }
 
         private int storeCalled;
         private int deleteCalled;
 
 
+        public FlowContext(IFlowHandlerContext handlerContext, FlowState flowState, IFlowStateLock flowStateLock)
+        {
+            this.flowState = flowState;
+            this.flowStateLock = flowStateLock;
+            this.handlerContext = handlerContext;
+        }
+
+
+        public FlowContext(IFlowHandlerContext handlerContext)
+        {
+            this.handlerContext = handlerContext;
+        }
+
+
+        public void SetFlowState(FlowState newFlowState, IFlowStateLock newFlowStateLock)
+        {
+            flowState = newFlowState;
+            flowStateLock = newFlowStateLock;
+        }
+
+
         public ValueTask Store(bool persistent)
         {
             storeCalled++;
 
-            if (HandlerContext == null) throw new ArgumentNullException(nameof(HandlerContext));
-            if (FlowState == null) throw new ArgumentNullException(nameof(FlowState));
-            if (FlowStateLock == null) throw new ArgumentNullException(nameof(FlowStateLock));
-
             FlowState.Data = Newtonsoft.Json.JsonConvert.SerializeObject(HandlerContext.Controller);
             return FlowStateLock.StoreFlowState(FlowState, persistent);
         }
@@ -32,7 +56,7 @@ namespace Tapeti.Flow.Default
         public ValueTask Delete()
         {
             deleteCalled++;
-            return FlowStateLock?.DeleteFlowState() ?? default;
+            return flowStateLock?.DeleteFlowState() ?? default;
         }
 
         public bool IsStoredOrDeleted()
@@ -43,7 +67,7 @@ namespace Tapeti.Flow.Default
         public void EnsureStoreOrDeleteIsCalled()
         {
             if (!IsStoredOrDeleted())
-                throw new InvalidProgramException("Neither Store nor Delete are called for the state of the current flow. FlowID = " + FlowStateLock?.FlowID);
+                throw new InvalidProgramException("Neither Store nor Delete are called for the state of the current flow. FlowID = " + flowStateLock?.FlowID);
 
             Debug.Assert(storeCalled <= 1, "Store called more than once!");
             Debug.Assert(deleteCalled <= 1, "Delete called more than once!");
@@ -51,7 +75,7 @@ namespace Tapeti.Flow.Default
 
         public void Dispose()
         {
-            FlowStateLock?.Dispose();
+            flowStateLock?.Dispose();
         }
     }
 }

Tapeti.Flow/Default/FlowContinuationMiddleware.cs

@@ -34,7 +34,11 @@ namespace Tapeti.Flow.Default
 
             if (context.TryGet<FlowMessageContextPayload>(out var flowPayload))
             {
+                if (controllerPayload.Controller == null)
+                    throw new InvalidOperationException("Controller is not available (method is static?)");
+
                 var flowContext = flowPayload.FlowContext;
+                if (!string.IsNullOrEmpty(flowContext.FlowState.Data))
                     Newtonsoft.Json.JsonConvert.PopulateObject(flowContext.FlowState.Data, controllerPayload.Controller);
 
                 // Remove Continuation now because the IYieldPoint result handler will store the new state
@@ -65,11 +69,11 @@ namespace Tapeti.Flow.Default
 
             var flowContext = flowPayload.FlowContext;
 
-            if (flowContext.ContinuationMetadata.MethodName != MethodSerializer.Serialize(controllerPayload.Binding.Method))
+            if (flowContext.ContinuationMetadata == null || flowContext.ContinuationMetadata.MethodName != MethodSerializer.Serialize(controllerPayload.Binding.Method))
                 // Do not call when the controller method was filtered, if the same message has two methods
                 return;
 
-            if (flowContext.FlowStateLock != null)
+            if (flowContext.HasFlowStateAndLock)
             {
                 if (!flowContext.IsStoredOrDeleted())
                     // The exception strategy can set the consume result to Success. Instead, check if the yield point
@@ -82,7 +86,7 @@ namespace Tapeti.Flow.Default
 
 
 
-        private static async ValueTask<FlowContext> EnrichWithFlowContext(IMessageContext context)
+        private static async ValueTask<FlowContext?> EnrichWithFlowContext(IMessageContext context)
         {
             if (context.TryGet<FlowMessageContextPayload>(out var flowPayload))
                 return flowPayload.FlowContext;
@@ -106,13 +110,8 @@ namespace Tapeti.Flow.Default
             if (flowState == null)
                 return null;
 
-            var flowContext = new FlowContext
+            var flowContext = new FlowContext(new FlowHandlerContext(context), flowState, flowStateLock)
             {
-                HandlerContext = new FlowHandlerContext(context),
-
-                FlowStateLock = flowStateLock,
-                FlowState = flowState,
-
                 ContinuationID = continuationID,
                 ContinuationMetadata = flowState.Continuations.TryGetValue(continuationID, out var continuation) ? continuation : null
             };

Tapeti.Flow/Default/FlowHandlerContext.cs

@@ -10,8 +10,11 @@ namespace Tapeti.Flow.Default
     {
         /// <summary>
         /// </summary>
-        public FlowHandlerContext()
+        public FlowHandlerContext(ITapetiConfig config, object? controller, MethodInfo method)
         {
+            Config = config;
+            Controller = controller;
+            Method = method;
         }
 
 
@@ -19,11 +22,7 @@ namespace Tapeti.Flow.Default
         /// </summary>
         public FlowHandlerContext(IMessageContext source)
         {
-            if (source == null)
+            var controllerPayload = source.Get<ControllerMessageContextPayload>();
-                return;
-
-            if (!source.TryGet<ControllerMessageContextPayload>(out var controllerPayload))
-                return;
 
             Config = source.Config;
             Controller = controllerPayload.Controller;
@@ -38,15 +37,15 @@ namespace Tapeti.Flow.Default
         }
 
         /// <inheritdoc />
-        public ITapetiConfig Config { get; set; }
+        public ITapetiConfig Config { get; }
 
         /// <inheritdoc />
-        public object Controller { get; set; }
+        public object? Controller { get; }
 
         /// <inheritdoc />
-        public MethodInfo Method { get; set; }
+        public MethodInfo Method { get; }
 
         /// <inheritdoc />
-        public IMessageContext MessageContext { get; set; }
+        public IMessageContext? MessageContext { get; }
     }
 }

Tapeti.Flow/Default/FlowProvider.cs

@@ -32,21 +32,21 @@ namespace Tapeti.Flow.Default
 
 
         /// <inheritdoc />
-        public IYieldPoint YieldWithRequest<TRequest, TResponse>(TRequest message, Func<TResponse, Task<IYieldPoint>> responseHandler)
+        public IYieldPoint YieldWithRequest<TRequest, TResponse>(TRequest message, Func<TResponse, Task<IYieldPoint>> responseHandler) where TRequest : class where TResponse : class
         {
             var responseHandlerInfo = GetResponseHandlerInfo(config, message, responseHandler);
             return new DelegateYieldPoint(context => SendRequest(context, message, responseHandlerInfo));
         }
 
         /// <inheritdoc />
-        public IYieldPoint YieldWithRequest<TRequest, TResponse>(TRequest message, Func<TResponse, ValueTask<IYieldPoint>> responseHandler)
+        public IYieldPoint YieldWithRequest<TRequest, TResponse>(TRequest message, Func<TResponse, ValueTask<IYieldPoint>> responseHandler) where TRequest : class where TResponse : class
         {
             var responseHandlerInfo = GetResponseHandlerInfo(config, message, responseHandler);
             return new DelegateYieldPoint(context => SendRequest(context, message, responseHandlerInfo));
         }
 
         /// <inheritdoc />
-        public IYieldPoint YieldWithRequestSync<TRequest, TResponse>(TRequest message, Func<TResponse, IYieldPoint> responseHandler)
+        public IYieldPoint YieldWithRequestSync<TRequest, TResponse>(TRequest message, Func<TResponse, IYieldPoint> responseHandler) where TRequest : class where TResponse : class
         {
             var responseHandlerInfo = GetResponseHandlerInfo(config, message, responseHandler);
             return new DelegateYieldPoint(context => SendRequest(context, message, responseHandlerInfo));
@@ -59,7 +59,7 @@ namespace Tapeti.Flow.Default
         }
 
         /// <inheritdoc />
-        public IYieldPoint EndWithResponse<TResponse>(TResponse message)
+        public IYieldPoint EndWithResponse<TResponse>(TResponse message) where TResponse : class
         {
             return new DelegateYieldPoint(context => SendResponse(context, message));
         }
@@ -72,7 +72,7 @@ namespace Tapeti.Flow.Default
 
 
         internal async Task SendRequest(FlowContext context, object message, ResponseHandlerInfo responseHandlerInfo, 
-            string convergeMethodName = null, bool convergeMethodTaskSync = false, bool store = true)
+            string? convergeMethodName = null, bool convergeMethodTaskSync = false, bool store = true)
         {
             if (context.FlowState == null)
             {
@@ -105,9 +105,9 @@ namespace Tapeti.Flow.Default
 
         private async Task SendResponse(FlowContext context, object message)
         {
-            var reply = context.FlowState == null
+            var reply = context.HasFlowStateAndLock
-                ? GetReply(context.HandlerContext)
+                ? context.FlowState.Metadata.Reply
-                : context.FlowState.Metadata.Reply;
+                : GetReply(context.HandlerContext);
 
             if (reply == null)
                 throw new YieldPointException("No response is required");
@@ -134,7 +134,7 @@ namespace Tapeti.Flow.Default
         {
             await context.Delete();
 
-            if (context.FlowState?.Metadata.Reply != null)
+            if (context.HasFlowStateAndLock && context.FlowState.Metadata.Reply != null)
                 throw new YieldPointException($"Flow must end with a response message of type {context.FlowState.Metadata.Reply.ResponseTypeName}");
         }
 
@@ -159,16 +159,15 @@ namespace Tapeti.Flow.Default
             if (binding.QueueName == null)
                 throw new ArgumentException("responseHandler is not yet subscribed to a queue, TapetiConnection.Subscribe must be called before starting a flow", nameof(responseHandler));
 
-            return new ResponseHandlerInfo
+            return new ResponseHandlerInfo(
-            {
+                MethodSerializer.Serialize(responseHandler.Method),
-                MethodName = MethodSerializer.Serialize(responseHandler.Method),
+                binding.QueueName,
-                ReplyToQueue = binding.QueueName,
+                binding.QueueType == QueueType.Durable
-                IsDurableQueue = binding.QueueType == QueueType.Durable
+            );
-            };
         }
 
 
-        private static ReplyMetadata GetReply(IFlowHandlerContext context)
+        private static ReplyMetadata? GetReply(IFlowHandlerContext context)
         {
             var requestAttribute = context.MessageContext?.Message?.GetType().GetCustomAttribute<RequestAttribute>();
             if (requestAttribute?.Response == null)
@@ -176,7 +175,7 @@ namespace Tapeti.Flow.Default
 
             return new ReplyMetadata
             {
-                CorrelationId = context.MessageContext.Properties.CorrelationId,
+                CorrelationId = context.MessageContext!.Properties.CorrelationId,
                 ReplyTo = context.MessageContext.Properties.ReplyTo,
                 ResponseTypeName = requestAttribute.Response.FullName,
                 Mandatory = context.MessageContext.Properties.Persistent.GetValueOrDefault(true)
@@ -188,18 +187,17 @@ namespace Tapeti.Flow.Default
             var flowStore = flowContext.HandlerContext.Config.DependencyResolver.Resolve<IFlowStore>();
 
             var flowID = Guid.NewGuid();
-            flowContext.FlowStateLock = await flowStore.LockFlowState(flowID);
+            var flowStateLock = await flowStore.LockFlowState(flowID);
 
-            if (flowContext.FlowStateLock == null)
+            if (flowStateLock == null)
                 throw new InvalidOperationException("Unable to lock a new flow");
 
-            flowContext.FlowState = new FlowState
+            var flowState = new FlowState
             {
-                Metadata = new FlowMetadata
+                Metadata = new FlowMetadata(GetReply(flowContext.HandlerContext))
-                {
-                    Reply = GetReply(flowContext.HandlerContext)
-                }
             };
+
+            flowContext.SetFlowState(flowState, flowStateLock);
         }
 
         
@@ -207,20 +205,16 @@ namespace Tapeti.Flow.Default
         public async ValueTask Execute(IFlowHandlerContext context, IYieldPoint yieldPoint)
         {
             if (yieldPoint is not DelegateYieldPoint executableYieldPoint)
-                throw new YieldPointException($"Yield point is required in controller {context.Controller.GetType().Name} for method {context.Method.Name}");
+                throw new YieldPointException($"Yield point is required in controller {context.Controller?.GetType().Name} for method {context.Method.Name}");
 
-            FlowContext flowContext = null;
+            FlowContext? flowContext = null;
             var disposeFlowContext = false;
 
             try
             {
-                var messageContext = context.MessageContext;
+                if (context.MessageContext == null || !context.MessageContext.TryGet<FlowMessageContextPayload>(out var flowPayload))
-                if (messageContext == null || !messageContext.TryGet<FlowMessageContextPayload>(out var flowPayload))
                 {
-                    flowContext = new FlowContext
+                    flowContext = new FlowContext(context);
-                    {
-                        HandlerContext = context
-                    };
 
                     // If we ended up here it is because of a Start. No point in storing the new FlowContext
                     // in the messageContext as the yield point is the last to execute.
@@ -236,7 +230,7 @@ namespace Tapeti.Flow.Default
                 catch (YieldPointException e)
                 {
                     // Useful for debugging
-                    e.Data["Tapeti.Controller.Name"] = context.Controller.GetType().FullName;
+                    e.Data["Tapeti.Controller.Name"] = context.Controller?.GetType().FullName;
                     e.Data["Tapeti.Controller.Method"] = context.Method.Name;
                     throw;
                 }
@@ -246,15 +240,15 @@ namespace Tapeti.Flow.Default
             finally
             {
                 if (disposeFlowContext)
-                    flowContext.Dispose();
+                    flowContext?.Dispose();
             }
         }
 
 
         /// <inheritdoc />
-        public IFlowParallelRequest GetParallelRequest(IFlowHandlerContext context)
+        public IFlowParallelRequest? GetParallelRequest(IFlowHandlerContext context)
         {
-            return context.MessageContext.TryGet<FlowMessageContextPayload>(out var flowPayload)
+            return context.MessageContext != null && context.MessageContext.TryGet<FlowMessageContextPayload>(out var flowPayload)
                 ? new ParallelRequest(config, this, flowPayload.FlowContext)
                 : null;
         }
@@ -263,27 +257,49 @@ namespace Tapeti.Flow.Default
         /// <inheritdoc />
         public ValueTask Converge(IFlowHandlerContext context)
         {
-            return Execute(context, new DelegateYieldPoint(flowContext => 
+            return Execute(context, new DelegateYieldPoint(async flowContext =>
-                Converge(flowContext, flowContext.ContinuationMetadata.ConvergeMethodName, flowContext.ContinuationMetadata.ConvergeMethodSync)));
+            {
+                if (flowContext.ContinuationMetadata == null)
+                    throw new InvalidOperationException("Missing ContinuationMetadata in FlowContext");
+
+                if (flowContext.ContinuationMetadata.ConvergeMethodName == null)
+                    throw new InvalidOperationException("Missing ConvergeMethodName in FlowContext ContinuationMetadata");
+
+                await Converge(flowContext, flowContext.ContinuationMetadata.ConvergeMethodName, flowContext.ContinuationMetadata.ConvergeMethodSync);
+            }));
         }
 
 
         internal async Task Converge(FlowContext flowContext, string convergeMethodName, bool convergeMethodSync)
         {
-            IYieldPoint yieldPoint;
+            IYieldPoint? yieldPoint;
+
+            if (flowContext.HandlerContext == null)
+                throw new InvalidOperationException($"Missing HandleContext in FlowContext for converge method {convergeMethodName}");
+
+            if (flowContext.HandlerContext.MessageContext == null)
+                throw new InvalidOperationException($"Missing MessageContext in FlowContext for converge method {convergeMethodName}");
 
             if (!flowContext.HandlerContext.MessageContext.TryGet<ControllerMessageContextPayload>(out var controllerPayload))
                 throw new ArgumentException("Context does not contain a controller payload", nameof(flowContext));
 
+            if (controllerPayload.Controller == null)
+                throw new InvalidOperationException($"Controller is not available for converge method {convergeMethodName} (method is static?)");
 
             var method = controllerPayload.Controller.GetType().GetMethod(convergeMethodName, BindingFlags.NonPublic | BindingFlags.Instance);
             if (method == null)
                 throw new ArgumentException($"Unknown converge method in controller {controllerPayload.Controller.GetType().Name}: {convergeMethodName}");
 
             if (convergeMethodSync)
-                yieldPoint = (IYieldPoint)method.Invoke(controllerPayload.Controller, new object[] { });
+                yieldPoint = (IYieldPoint?)method.Invoke(controllerPayload.Controller, new object[] { });
             else
-                yieldPoint = await(Task<IYieldPoint>)method.Invoke(controllerPayload.Controller, new object[] { });
+            {
+                var yieldPointTask = method.Invoke(controllerPayload.Controller, new object[] { });
+                if (yieldPointTask == null)
+                    throw new YieldPointException($"Yield point is required in controller {controllerPayload.Controller.GetType().Name} for converge method {convergeMethodName}");
+
+                yieldPoint = await (Task<IYieldPoint>)yieldPointTask;
+            }
 
             if (yieldPoint == null)
                 throw new YieldPointException($"Yield point is required in controller {controllerPayload.Controller.GetType().Name} for converge method {convergeMethodName}");
@@ -297,8 +313,15 @@ namespace Tapeti.Flow.Default
         {
             private class RequestInfo
             {
-                public object Message { get; init; }
+                public object Message { get; }
-                public ResponseHandlerInfo ResponseHandlerInfo { get; init; }
+                public ResponseHandlerInfo ResponseHandlerInfo { get; }
+
+                
+                public RequestInfo(object message, ResponseHandlerInfo responseHandlerInfo)
+                {
+                    Message = message;
+                    ResponseHandlerInfo = responseHandlerInfo;
+                }
             }
 
 
@@ -314,32 +337,32 @@ namespace Tapeti.Flow.Default
             }
 
 
-            public IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, Task> responseHandler)
+            public IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, Task> responseHandler) where TRequest : class where TResponse : class
             {
                 return InternalAddRequest(message, responseHandler);
             }
 
-            public IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, ValueTask> responseHandler)
+            public IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, ValueTask> responseHandler) where TRequest : class where TResponse : class
             {
                 return InternalAddRequest(message, responseHandler);
             }
 
-            public IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, IFlowParallelRequest, Task> responseHandler)
+            public IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, IFlowParallelRequest, Task> responseHandler) where TRequest : class where TResponse : class
             {
                 return InternalAddRequest(message, responseHandler);
             }
 
-            public IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, IFlowParallelRequest, ValueTask> responseHandler)
+            public IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, IFlowParallelRequest, ValueTask> responseHandler) where TRequest : class where TResponse : class
             {
                 return InternalAddRequest(message, responseHandler);
             }
 
-            public IFlowParallelRequestBuilder AddRequestSync<TRequest, TResponse>(TRequest message, Action<TResponse> responseHandler)
+            public IFlowParallelRequestBuilder AddRequestSync<TRequest, TResponse>(TRequest message, Action<TResponse> responseHandler) where TRequest : class where TResponse : class
             {
                 return InternalAddRequest(message, responseHandler);
             }
 
-            public IFlowParallelRequestBuilder AddRequestSync<TRequest, TResponse>(TRequest message, Action<TResponse, IFlowParallelRequest> responseHandler)
+            public IFlowParallelRequestBuilder AddRequestSync<TRequest, TResponse>(TRequest message, Action<TResponse, IFlowParallelRequest> responseHandler) where TRequest : class where TResponse : class
             {
                 return InternalAddRequest(message, responseHandler);
             }
@@ -347,12 +370,7 @@ namespace Tapeti.Flow.Default
 
             private IFlowParallelRequestBuilder InternalAddRequest(object message, Delegate responseHandler)
             {
-                requests.Add(new RequestInfo
+                requests.Add(new RequestInfo(message, GetResponseHandlerInfo(config, message, responseHandler)));
-                {
-                    Message = message,
-                    ResponseHandlerInfo = GetResponseHandlerInfo(config, message, responseHandler)
-                });
-
                 return this;
             }
 
@@ -381,12 +399,12 @@ namespace Tapeti.Flow.Default
                     };
                 }
 
-                if (convergeMethod?.Method == null)
+                if (convergeMethod.Method == null)
                     throw new ArgumentNullException(nameof(convergeMethod));
 
                 return new DelegateYieldPoint(async context =>
                 {
-                    if (convergeMethod.Method.DeclaringType != context.HandlerContext.Controller.GetType())
+                    if (convergeMethod.Method.DeclaringType != context.HandlerContext.Controller?.GetType())
                         throw new YieldPointException("Converge method must be in the same controller class");
 
                     await Task.WhenAll(requests.Select(requestInfo =>
@@ -419,19 +437,19 @@ namespace Tapeti.Flow.Default
             }
 
 
-            public Task AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, Task> responseHandler)
+            public Task AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, Task> responseHandler) where TRequest : class where TResponse : class
             {
                 return InternalAddRequest(message, responseHandler);
             }
 
 
-            public Task AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, IFlowParallelRequest, Task> responseHandler)
+            public Task AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, IFlowParallelRequest, Task> responseHandler) where TRequest : class where TResponse : class
             {
                 return InternalAddRequest(message, responseHandler);
             }
 
 
-            public Task AddRequestSync<TRequest, TResponse>(TRequest message, Action<TResponse> responseHandler)
+            public Task AddRequestSync<TRequest, TResponse>(TRequest message, Action<TResponse> responseHandler) where TRequest : class where TResponse : class
             {
                 return InternalAddRequest(message, responseHandler);
             }
@@ -441,6 +459,9 @@ namespace Tapeti.Flow.Default
             {
                 var responseHandlerInfo = GetResponseHandlerInfo(config, message, responseHandler);
 
+                if (flowContext.ContinuationMetadata == null)
+                    throw new InvalidOperationException("No ContinuationMetadata in FlowContext");
+
                 return flowProvider.SendRequest(
                     flowContext, 
                     message, 
@@ -454,9 +475,17 @@ namespace Tapeti.Flow.Default
 
         internal class ResponseHandlerInfo
         {
-            public string MethodName { get; set; }
+            public string MethodName { get; }
-            public string ReplyToQueue { get; set; }
+            public string ReplyToQueue { get; }
-            public bool IsDurableQueue { get; set; }
+            public bool IsDurableQueue { get; }
+
+
+            public ResponseHandlerInfo(string methodName, string replyToQueue, bool isDurableQueue)
+            {
+                MethodName = methodName;
+                ReplyToQueue = replyToQueue;
+                IsDurableQueue = isDurableQueue;
+            }
         }
     }
 }

Tapeti.Flow/Default/FlowStarter.cs

@@ -25,39 +25,38 @@ namespace Tapeti.Flow.Default
         /// <inheritdoc />
         public async Task Start<TController>(Expression<Func<TController, Func<IYieldPoint>>> methodSelector) where TController : class
         {
-            await CallControllerMethod<TController>(GetExpressionMethod(methodSelector), value => Task.FromResult((IYieldPoint)value), new object[] { });
+            await CallControllerMethod<TController>(GetExpressionMethod(methodSelector), value => Task.FromResult((IYieldPoint)value), Array.Empty<object?>());
         }
 
         /// <inheritdoc />
         public async Task Start<TController>(Expression<Func<TController, Func<Task<IYieldPoint>>>> methodSelector) where TController : class
         {
-            await CallControllerMethod<TController>(GetExpressionMethod(methodSelector), value => (Task<IYieldPoint>)value, new object[] {});
+            await CallControllerMethod<TController>(GetExpressionMethod(methodSelector), value => (Task<IYieldPoint>)value, Array.Empty<object?>());
         }
 
         /// <inheritdoc />
         public async Task Start<TController, TParameter>(Expression<Func<TController, Func<TParameter, IYieldPoint>>> methodSelector, TParameter parameter) where TController : class
         {
-            await CallControllerMethod<TController>(GetExpressionMethod(methodSelector), value => Task.FromResult((IYieldPoint)value), new object[] {parameter});
+            await CallControllerMethod<TController>(GetExpressionMethod(methodSelector), value => Task.FromResult((IYieldPoint)value), new object?[] {parameter});
         }
 
         /// <inheritdoc />
         public async Task Start<TController, TParameter>(Expression<Func<TController, Func<TParameter, Task<IYieldPoint>>>> methodSelector, TParameter parameter) where TController : class
         {
-            await CallControllerMethod<TController>(GetExpressionMethod(methodSelector), value => (Task<IYieldPoint>)value, new object[] {parameter});
+            await CallControllerMethod<TController>(GetExpressionMethod(methodSelector), value => (Task<IYieldPoint>)value, new object?[] {parameter});
         }
 
 
-        private async Task CallControllerMethod<TController>(MethodInfo method, Func<object, Task<IYieldPoint>> getYieldPointResult, object[] parameters) where TController : class
+        private async Task CallControllerMethod<TController>(MethodInfo method, Func<object, Task<IYieldPoint>> getYieldPointResult, object?[] parameters) where TController : class
         {
             var controller = config.DependencyResolver.Resolve<TController>();
-            var yieldPoint = await getYieldPointResult(method.Invoke(controller, parameters));
+            var result = method.Invoke(controller, parameters);
+            if (result == null)
+                throw new InvalidOperationException($"Method {method.Name} must return an IYieldPoint or Task<IYieldPoint>, got null");
 
-            var context = new FlowHandlerContext
+            var yieldPoint = await getYieldPointResult(result);
-            {
+
-                Config = config,
+            var context = new FlowHandlerContext(config, controller, method);
-                Controller = controller,
-                Method = method
-            };
 
             var flowHandler = config.DependencyResolver.Resolve<IFlowHandler>();
             await flowHandler.Execute(context, yieldPoint);

Tapeti.Flow/Default/FlowState.cs

@@ -9,8 +9,8 @@ namespace Tapeti.Flow.Default
     /// </summary>
     public class FlowState
     {
-        private FlowMetadata metadata;
+        private FlowMetadata? metadata;
-        private Dictionary<Guid, ContinuationMetadata> continuations;
+        private Dictionary<Guid, ContinuationMetadata>? continuations;
 
 
         /// <summary>
@@ -18,7 +18,7 @@ namespace Tapeti.Flow.Default
         /// </summary>
         public FlowMetadata Metadata
         {
-            get => metadata ??= new FlowMetadata();
+            get => metadata ??= new FlowMetadata(null);
             set => metadata = value;
         }
 
@@ -26,7 +26,7 @@ namespace Tapeti.Flow.Default
         /// <summary>
         /// Contains the serialized state which is restored when a flow continues.
         /// </summary>
-        public string Data { get; set; }
+        public string? Data { get; set; }
 
 
         /// <summary>
@@ -45,7 +45,7 @@ namespace Tapeti.Flow.Default
         public FlowState Clone()
         {
             return new FlowState {
-                metadata = metadata.Clone(),
+                metadata = metadata?.Clone(),
                 Data = Data,
                 continuations = continuations?.ToDictionary(kv => kv.Key, kv => kv.Value.Clone())
             };
@@ -61,7 +61,14 @@ namespace Tapeti.Flow.Default
         /// <summary>
         /// Contains information about the expected response for this flow.
         /// </summary>
-        public ReplyMetadata Reply { get; set; }
+        public ReplyMetadata? Reply { get; }
+
+
+        /// <inheritdoc cref="FlowMetadata"/>
+        public FlowMetadata(ReplyMetadata? reply)
+        {
+            Reply = reply;
+        }
 
         
         /// <summary>
@@ -69,10 +76,7 @@ namespace Tapeti.Flow.Default
         /// </summary>
         public FlowMetadata Clone()
         {
-            return new FlowMetadata
+            return new FlowMetadata(Reply);
-            {
-                Reply = Reply?.Clone()
-            };
         }
     }
 
@@ -85,17 +89,17 @@ namespace Tapeti.Flow.Default
         /// <summary>
         /// The queue to which the response should be sent.
         /// </summary>
-        public string ReplyTo { get; set; }
+        public string? ReplyTo { get; set; }
 
         /// <summary>
         /// The correlation ID included in the original request.
         /// </summary>
-        public string CorrelationId { get; set; }
+        public string? CorrelationId { get; set; }
 
         /// <summary>
         /// The expected response message class.
         /// </summary>
-        public string ResponseTypeName { get; set; }
+        public string? ResponseTypeName { get; set; }
 
         /// <summary>
         /// Indicates whether the response should be sent a mandatory.
@@ -128,12 +132,12 @@ namespace Tapeti.Flow.Default
         /// <summary>
         /// The name of the method which will handle the response.
         /// </summary>
-        public string MethodName { get; set; }
+        public string? MethodName { get; set; }
 
         /// <summary>
         /// The name of the method which is called when all responses have been processed.
         /// </summary>
-        public string ConvergeMethodName { get; set; }
+        public string? ConvergeMethodName { get; set; }
 
         /// <summary>
         /// Determines if the converge method is synchronous or asynchronous.

Tapeti.Flow/Default/FlowStore.cs

@@ -16,11 +16,11 @@ namespace Tapeti.Flow.Default
     {
         private class CachedFlowState
         {
-            public readonly FlowState FlowState;
+            public readonly FlowState? FlowState;
             public readonly DateTime CreationTime;
             public readonly bool IsPersistent;
 
-            public CachedFlowState(FlowState flowState, DateTime creationTime, bool isPersistent)
+            public CachedFlowState(FlowState? flowState, DateTime creationTime, bool isPersistent)
             {
                 FlowState = flowState;
                 CreationTime = creationTime;
@@ -31,7 +31,7 @@ namespace Tapeti.Flow.Default
         private readonly ConcurrentDictionary<Guid, CachedFlowState> flowStates = new();
         private readonly ConcurrentDictionary<Guid, Guid> continuationLookup = new();
         private readonly LockCollection<Guid> locks = new(EqualityComparer<Guid>.Default);
-        private HashSet<string> validatedMethods;
+        private HashSet<string>? validatedMethods;
 
         private readonly IFlowRepository repository;
         private readonly ITapetiConfig config;
@@ -85,10 +85,13 @@ namespace Tapeti.Flow.Default
 
         private void ValidateContinuation(Guid flowId, Guid continuationId, ContinuationMetadata metadata)
         {
+            if (string.IsNullOrEmpty(metadata.MethodName))
+                return;
+
             // We could check all the things that are required for a continuation or converge method, but this should suffice
             // for the common scenario where you change code without realizing that it's signature has been persisted
             // ReSharper disable once InvertIf
-            if (validatedMethods.Add(metadata.MethodName))
+            if (validatedMethods!.Add(metadata.MethodName))
             {
                 var methodInfo = MethodSerializer.Deserialize(metadata.MethodName);
                 if (methodInfo == null)
@@ -150,8 +153,8 @@ namespace Tapeti.Flow.Default
         private class FlowStateLock : IFlowStateLock
         {
             private readonly FlowStore owner;
-            private volatile IDisposable flowLock;
+            private volatile IDisposable? flowLock;
-            private CachedFlowState cachedFlowState;
+            private CachedFlowState? cachedFlowState;
 
             public Guid FlowID { get; }
 
@@ -172,12 +175,12 @@ namespace Tapeti.Flow.Default
                 l?.Dispose();
             }
 
-            public ValueTask<FlowState> GetFlowState()
+            public ValueTask<FlowState?> GetFlowState()
             {
                 if (flowLock == null)
                     throw new ObjectDisposedException("FlowStateLock");
 
-                return new ValueTask<FlowState>(cachedFlowState?.FlowState?.Clone());
+                return new ValueTask<FlowState?>(cachedFlowState?.FlowState?.Clone());
             }
 
             public async ValueTask StoreFlowState(FlowState newFlowState, bool persistent)
@@ -189,13 +192,13 @@ namespace Tapeti.Flow.Default
                 newFlowState = newFlowState.Clone();
 
                 // Update the lookup dictionary for the ContinuationIDs
-                if (cachedFlowState != null)
+                if (cachedFlowState?.FlowState != null)
                 {
                     foreach (var removedContinuation in cachedFlowState.FlowState.Continuations.Keys.Where(k => !newFlowState.Continuations.ContainsKey(k)))
                         owner.continuationLookup.TryRemove(removedContinuation, out _);
                 }
 
-                foreach (var addedContinuation in newFlowState.Continuations.Where(c => cachedFlowState == null || !cachedFlowState.FlowState.Continuations.ContainsKey(c.Key)))
+                foreach (var addedContinuation in newFlowState.Continuations.Where(c => cachedFlowState?.FlowState == null || !cachedFlowState.FlowState.Continuations.ContainsKey(c.Key)))
                 {
                     owner.continuationLookup.TryAdd(addedContinuation.Key, FlowID);
                 }
@@ -203,7 +206,7 @@ namespace Tapeti.Flow.Default
                 var isNew = cachedFlowState == null;
                 var wasPersistent = cachedFlowState?.IsPersistent ?? false;
 
-                cachedFlowState = new CachedFlowState(newFlowState, isNew ? DateTime.UtcNow : cachedFlowState.CreationTime, persistent);
+                cachedFlowState = new CachedFlowState(newFlowState, isNew ? DateTime.UtcNow : cachedFlowState!.CreationTime, persistent);
                 owner.flowStates[FlowID] = cachedFlowState;
 
                 if (persistent)
@@ -231,7 +234,7 @@ namespace Tapeti.Flow.Default
                 if (flowLock == null)
                     throw new ObjectDisposedException("FlowStateLock");
 
-                if (cachedFlowState != null)
+                if (cachedFlowState?.FlowState != null)
                 {
                     foreach (var removedContinuation in cachedFlowState.FlowState.Continuations.Keys)
                         owner.continuationLookup.TryRemove(removedContinuation, out _);
@@ -239,7 +242,7 @@ namespace Tapeti.Flow.Default
                     owner.flowStates.TryRemove(FlowID, out var removedFlowState);
                     cachedFlowState = null;
 
-                    if (removedFlowState.IsPersistent)
+                    if (removedFlowState is { IsPersistent: true })
                         await owner.repository.DeleteState(FlowID);
                 }
             }

Tapeti.Flow/FlowExtension.cs

@@ -9,11 +9,11 @@ namespace Tapeti.Flow
     /// </summary>
     public class FlowExtension : ITapetiExtension
     {
-        private readonly IFlowRepository flowRepository;
+        private readonly IFlowRepository? flowRepository;
 
         /// <summary>
         /// </summary>
-        public FlowExtension(IFlowRepository flowRepository)
+        public FlowExtension(IFlowRepository? flowRepository)
         {
             this.flowRepository = flowRepository;
         }

Tapeti.Flow/FlowHelpers/LockCollection.cs

@@ -7,7 +7,7 @@ namespace Tapeti.Flow.FlowHelpers
     /// <summary>
     /// Implementation of an asynchronous locking mechanism.
     /// </summary>
-    public class LockCollection<T>
+    public class LockCollection<T> where T : notnull
     {
         private readonly Dictionary<T, LockItem> locks;
 
@@ -57,7 +57,7 @@ namespace Tapeti.Flow.FlowHelpers
 
         private class LockItem : IDisposable
         {
-            internal volatile LockItem Next;
+            internal volatile LockItem? Next;
 
             private readonly Dictionary<T, LockItem> locks;
             private readonly TaskCompletionSource<IDisposable> tcs = new(TaskCreationOptions.RunContinuationsAsynchronously);

Tapeti.Flow/FlowHelpers/MethodSerializer.cs

@@ -25,7 +25,7 @@ namespace Tapeti.Flow.FlowHelpers
         /// Deserializes the serialized method representation back into it's MethodInfo, or null if not found.
         /// </summary>
         /// <param name="serializedMethod"></param>
-        public static MethodInfo Deserialize(string serializedMethod)
+        public static MethodInfo? Deserialize(string serializedMethod)
         {
             var match = DeserializeRegex.Match(serializedMethod);
             if (!match.Success)

Tapeti.Flow/FlowMessageContextPayload.cs

@@ -16,9 +16,8 @@ namespace Tapeti.Flow
         /// parallel flow is done and the convergeMethod will be called.
         /// Temporarily disables storing the flow state.
         /// </summary>
-        public bool FlowIsConverging => FlowContext != null && 
+        public bool FlowIsConverging => FlowContext.FlowState.Continuations.Count == 0 &&
-                                        FlowContext.FlowState.Continuations.Count == 0 &&
+                                        FlowContext.ContinuationMetadata?.ConvergeMethodName != null;
-                                        FlowContext.ContinuationMetadata.ConvergeMethodName != null;
 
         
         public FlowMessageContextPayload(FlowContext flowContext)
@@ -29,7 +28,7 @@ namespace Tapeti.Flow
         
         public void Dispose()
         {
-            FlowContext?.Dispose();
+            FlowContext.Dispose();
         }
     }
 }

Tapeti.Flow/IFlowHandlerContext.cs

@@ -18,7 +18,7 @@ namespace Tapeti.Flow
         /// <summary>
         /// An instance of the controller which starts or continues the flow.
         /// </summary>
-        object Controller { get; }
+        object? Controller { get; }
 
 
         /// <summary>
@@ -31,6 +31,6 @@ namespace Tapeti.Flow
         /// Access to the message context if this is a continuated flow.
         /// Will be null when in a starting flow.
         /// </summary>
-        IMessageContext MessageContext { get; }
+        IMessageContext? MessageContext { get; }
     }
 }

Tapeti.Flow/IFlowProvider.cs

@@ -20,7 +20,7 @@ namespace Tapeti.Flow
         /// <param name="responseHandler"></param>
         /// <typeparam name="TRequest"></typeparam>
         /// <typeparam name="TResponse"></typeparam>
-        IYieldPoint YieldWithRequest<TRequest, TResponse>(TRequest message, Func<TResponse, Task<IYieldPoint>> responseHandler);
+        IYieldPoint YieldWithRequest<TRequest, TResponse>(TRequest message, Func<TResponse, Task<IYieldPoint>> responseHandler) where TRequest : class where TResponse : class;
 
 
         /// <summary>
@@ -32,7 +32,7 @@ namespace Tapeti.Flow
         /// <param name="responseHandler"></param>
         /// <typeparam name="TRequest"></typeparam>
         /// <typeparam name="TResponse"></typeparam>
-        IYieldPoint YieldWithRequest<TRequest, TResponse>(TRequest message, Func<TResponse, ValueTask<IYieldPoint>> responseHandler);
+        IYieldPoint YieldWithRequest<TRequest, TResponse>(TRequest message, Func<TResponse, ValueTask<IYieldPoint>> responseHandler) where TRequest : class where TResponse : class;
 
 
         /// <summary>
@@ -51,7 +51,7 @@ namespace Tapeti.Flow
         /// <typeparam name="TRequest"></typeparam>
         /// <typeparam name="TResponse"></typeparam>
         /// <returns></returns>
-        IYieldPoint YieldWithRequestSync<TRequest, TResponse>(TRequest message, Func<TResponse, IYieldPoint> responseHandler);
+        IYieldPoint YieldWithRequestSync<TRequest, TResponse>(TRequest message, Func<TResponse, IYieldPoint> responseHandler) where TRequest : class where TResponse : class;
 
 
         /// <summary>
@@ -67,7 +67,7 @@ namespace Tapeti.Flow
         /// </summary>
         /// <param name="message"></param>
         /// <typeparam name="TResponse"></typeparam>
-        IYieldPoint EndWithResponse<TResponse>(TResponse message);
+        IYieldPoint EndWithResponse<TResponse>(TResponse message) where TResponse : class;
 
 
         /// <summary>
@@ -126,7 +126,7 @@ namespace Tapeti.Flow
         /// <summary>
         /// Returns the parallel request for the given message context.
         /// </summary>
-        IFlowParallelRequest GetParallelRequest(IFlowHandlerContext context);
+        IFlowParallelRequest? GetParallelRequest(IFlowHandlerContext context);
 
 
         /// <summary>
@@ -174,7 +174,7 @@ namespace Tapeti.Flow
         /// </summary>
         /// <param name="message"></param>
         /// <param name="responseHandler"></param>
-        IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, Task> responseHandler);
+        IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, Task> responseHandler) where TRequest : class where TResponse : class;
 
         /// <summary>
         /// Publish a request message and continue the flow when the response arrives.
@@ -184,21 +184,21 @@ namespace Tapeti.Flow
         /// </summary>
         /// <param name="message"></param>
         /// <param name="responseHandler"></param>
-        IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, ValueTask> responseHandler);
+        IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, ValueTask> responseHandler) where TRequest : class where TResponse : class;
 
         /// <remarks>
         /// This overload allows the response handler access to the IFlowParallelRequest interface, which
         /// can be used to add additional requests to the parallel request before the continuation method passed to the Yield method is called.
         /// </remarks>
         /// <inheritdoc cref="AddRequest{TRequest,TResponse}(TRequest,Func{TResponse,Task})"/>
-        IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, IFlowParallelRequest, Task> responseHandler);
+        IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, IFlowParallelRequest, Task> responseHandler) where TRequest : class where TResponse : class;
 
         /// <remarks>
         /// This overload allows the response handler access to the IFlowParallelRequest interface, which
         /// can be used to add additional requests to the parallel request before the continuation method passed to the Yield method is called.
         /// </remarks>
         /// <inheritdoc cref="AddRequest{TRequest,TResponse}(TRequest,Func{TResponse,ValueTask})"/>
-        IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, IFlowParallelRequest, ValueTask> responseHandler);
+        IFlowParallelRequestBuilder AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, IFlowParallelRequest, ValueTask> responseHandler) where TRequest : class where TResponse : class;
 
         /// <summary>
         /// Publish a request message and continue the flow when the response arrives.
@@ -208,14 +208,14 @@ namespace Tapeti.Flow
         /// </summary>
         /// <param name="message"></param>
         /// <param name="responseHandler"></param>
-        IFlowParallelRequestBuilder AddRequestSync<TRequest, TResponse>(TRequest message, Action<TResponse> responseHandler);
+        IFlowParallelRequestBuilder AddRequestSync<TRequest, TResponse>(TRequest message, Action<TResponse> responseHandler) where TRequest : class where TResponse : class;
 
         /// <remarks>
         /// This overload allows the response handler access to the IFlowParallelRequest interface, which
         /// can be used to add additional requests to the parallel request before the continuation method passed to the Yield method is called.
         /// </remarks>
         /// <inheritdoc cref="AddRequestSync{TRequest,TResponse}(TRequest,Action{TResponse})"/>
-        IFlowParallelRequestBuilder AddRequestSync<TRequest, TResponse>(TRequest message, Action<TResponse, IFlowParallelRequest> responseHandler);
+        IFlowParallelRequestBuilder AddRequestSync<TRequest, TResponse>(TRequest message, Action<TResponse, IFlowParallelRequest> responseHandler) where TRequest : class where TResponse : class;
 
         /// There is no Sync overload with an IFlowParallelRequest parameter, as the AddRequest methods for that are
         /// async, so you should always await them.
@@ -260,14 +260,14 @@ namespace Tapeti.Flow
         /// </summary>
         /// <param name="message"></param>
         /// <param name="responseHandler"></param>
-        Task AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, Task> responseHandler);
+        Task AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, Task> responseHandler) where TRequest : class where TResponse : class;
 
         /// <remarks>
         /// This overload allows the response handler access to the IFlowParallelRequest interface, which
         /// can be used to add additional requests to the parallel request before the continuation method passed to the Yield method is called.
         /// </remarks>
         /// <inheritdoc cref="AddRequest{TRequest,TResponse}(TRequest,Func{TResponse,Task})"/>
-        Task AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, IFlowParallelRequest, Task> responseHandler);
+        Task AddRequest<TRequest, TResponse>(TRequest message, Func<TResponse, IFlowParallelRequest, Task> responseHandler) where TRequest : class where TResponse : class;
 
         /// <summary>
         /// Publish a request message and continue the flow when the response arrives.
@@ -277,7 +277,7 @@ namespace Tapeti.Flow
         /// </summary>
         /// <param name="message"></param>
         /// <param name="responseHandler"></param>
-        Task AddRequestSync<TRequest, TResponse>(TRequest message, Action<TResponse> responseHandler);
+        Task AddRequestSync<TRequest, TResponse>(TRequest message, Action<TResponse> responseHandler) where TRequest : class where TResponse : class;
     }
 
 

Tapeti.Flow/IFlowStore.cs

@@ -55,7 +55,7 @@ namespace Tapeti.Flow
         /// <summary>
         /// Acquires a copy of the flow state.
         /// </summary>
-        ValueTask<FlowState> GetFlowState();
+        ValueTask<FlowState?> GetFlowState();
 
         /// <summary>
         /// Stores the new flow state.

Tapeti.Flow/ReSharper/JetBrains.Annotations.cs

@@ -170,11 +170,11 @@ namespace JetBrains.Annotations
     {
         public PublicAPIAttribute() { }
 
-        public PublicAPIAttribute([NotNull] string comment)
+        public PublicAPIAttribute(string comment)
         {
             Comment = comment;
         }
 
-        [CanBeNull] public string Comment { get; }
+        public string? Comment { get; }
     }
 }

Tapeti.Flow/Tapeti.Flow.csproj

@@ -12,6 +12,7 @@
     <PackageIcon>Tapeti.Flow.png</PackageIcon>
     <Version>2.0.0</Version>
     <LangVersion>9</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">

Tapeti.Ninject/Tapeti.Ninject.csproj

@@ -12,6 +12,7 @@
     <PackageIcon>Tapeti.SimpleInjector.png</PackageIcon>
     <Version>2.0.0</Version>
     <LangVersion>9</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

Tapeti.Serilog/Middleware/MessageHandlerLoggingBindingMiddleware.cs

@@ -43,7 +43,7 @@ namespace Tapeti.Serilog.Middleware
         }
 
 
-        private static object DiagnosticContextFactory(IMessageContext context)
+        private static object? DiagnosticContextFactory(IMessageContext context)
         {
             return context.TryGet<DiagnosticContextPayload>(out var diagnosticContextPayload)
                 ? diagnosticContextPayload.DiagnosticContext

Tapeti.Serilog/Tapeti.Serilog.csproj

@@ -12,6 +12,7 @@
     <PackageIcon>Tapeti.Serilog.png</PackageIcon>
     <Version>2.0.0</Version>
     <LangVersion>9</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">

Tapeti.Serilog/TapetiSeriLogger.cs

@@ -87,7 +87,7 @@ namespace Tapeti.Serilog
         public void ConsumeException(Exception exception, IMessageContext messageContext, ConsumeResult consumeResult)
         {
             var message = new StringBuilder("Tapeti: exception in message handler");
-            var messageParams = new List<object>();
+            var messageParams = new List<object?>();
             
             var contextLogger = seriLogger
                 .ForContext("consumeResult", consumeResult)
@@ -130,7 +130,7 @@ namespace Tapeti.Serilog
         }
 
         /// <inheritdoc />
-        public void QueueExistsWarning(string queueName, IRabbitMQArguments existingArguments, IRabbitMQArguments arguments)
+        public void QueueExistsWarning(string queueName, IRabbitMQArguments? existingArguments, IRabbitMQArguments? arguments)
         {
             seriLogger.Warning("Tapeti: durable queue {queueName} exists with incompatible x-arguments ({existingArguments} vs. {arguments}) and will not be redeclared, queue will be consumed as-is",
                 queueName,

Tapeti.SimpleInjector/SimpleInjectorDependencyResolver.cs

@@ -10,12 +10,12 @@ namespace Tapeti.SimpleInjector
     public class SimpleInjectorDependencyResolver : IDependencyContainer
     {
         private readonly Container container;
-        private readonly Lifestyle defaultsLifestyle;
+        private readonly Lifestyle? defaultsLifestyle;
-        private readonly Lifestyle controllersLifestyle;
+        private readonly Lifestyle? controllersLifestyle;
 
         /// <summary>
         /// </summary>
-        public SimpleInjectorDependencyResolver(Container container, Lifestyle defaultsLifestyle = null, Lifestyle controllersLifestyle = null)
+        public SimpleInjectorDependencyResolver(Container container, Lifestyle? defaultsLifestyle = null, Lifestyle? controllersLifestyle = null)
         {
             this.container = container;
             this.defaultsLifestyle = defaultsLifestyle;

Tapeti.SimpleInjector/Tapeti.SimpleInjector.csproj

@@ -12,6 +12,7 @@
     <PackageIcon>Tapeti.SimpleInjector.png</PackageIcon>
     <Version>2.0.0</Version>
     <LangVersion>9</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">

Tapeti.Tests/Client/RabbitMQFixture.cs

@@ -27,7 +27,7 @@ namespace Tapeti.Tests.Client
         public ushort RabbitMQManagementPort { get; private set; }
 
 
-        private TestcontainerMessageBroker testcontainers;
+        private TestcontainerMessageBroker? testcontainers;
 
         private const int DefaultRabbitMQPort = 5672;
         private const int DefaultRabbitMQManagementPort = 15672;

Tapeti.Tests/Client/TapetiClientTests.cs

@@ -19,7 +19,7 @@ namespace Tapeti.Tests.Client
         private readonly RabbitMQFixture fixture;
         private readonly MockDependencyResolver dependencyResolver = new();
 
-        private TapetiClient client;
+        private TapetiClient client = null!;
 
 
         public TapetiClientTests(RabbitMQFixture fixture, ITestOutputHelper testOutputHelper)
@@ -41,7 +41,6 @@ namespace Tapeti.Tests.Client
         public async Task DisposeAsync()
         {
             await client.Close();
-            client = null;
         }
 
 

Tapeti.Tests/Config/QueueArgumentsTest.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using FluentAssertions;
@@ -13,6 +14,16 @@ using Xunit;
 
 namespace Tapeti.Tests.Config
 {
+    internal static class UTF8StringExtensions
+    {
+        public static string AsUTF8String(this object value)
+        {
+            value.Should().BeOfType<byte[]>();
+            return Encoding.UTF8.GetString((byte[])value);
+        }
+    }
+
+
     public class QueueArgumentsTest : BaseControllerTest
     {
         private static readonly MockRepository MoqRepository = new(MockBehavior.Strict);
@@ -88,12 +99,12 @@ namespace Tapeti.Tests.Config
             declaredQueues.Should().HaveCount(1);
             var arguments = declaredQueues["queue-1"];
 
-            arguments.Should().ContainKey("x-custom").WhoseValue.Should().Be("custom value");
+            arguments.Should().ContainKey("x-custom").WhoseValue.AsUTF8String().Should().Be("custom value");
             arguments.Should().ContainKey("x-another").WhoseValue.Should().Be(true);
             arguments.Should().ContainKey("x-max-length").WhoseValue.Should().Be(100);
             arguments.Should().ContainKey("x-max-length-bytes").WhoseValue.Should().Be(100000);
             arguments.Should().ContainKey("x-message-ttl").WhoseValue.Should().Be(4269);
-            arguments.Should().ContainKey("x-overflow").WhoseValue.Should().Be("reject-publish");
+            arguments.Should().ContainKey("x-overflow").WhoseValue.AsUTF8String().Should().Be("reject-publish");
         }
 
 

Tapeti.Tests/Mock/MockDependencyResolver.cs

@@ -8,7 +8,7 @@ namespace Tapeti.Tests.Mock
         private readonly Dictionary<Type, object> container = new();
 
 
-        public void Set<TInterface>(TInterface instance)
+        public void Set<TInterface>(TInterface instance) where TInterface : class
         {
             container.Add(typeof(TInterface), instance);
         }

Tapeti.Tests/Mock/MockLogger.cs

@@ -49,8 +49,17 @@ namespace Tapeti.Tests.Mock
                 : $"Declaring {(durable ? "durable" : "dynamic")} queue {queueName}");
         }
 
-        public void QueueExistsWarning(string queueName, IRabbitMQArguments existingArguments, IRabbitMQArguments arguments)
+        public void QueueExistsWarning(string queueName, IRabbitMQArguments? existingArguments, IRabbitMQArguments? arguments)
         {
+            testOutputHelper.WriteLine($"[Tapeti] Durable queue {queueName} exists with incompatible x-arguments ({GetArgumentsText(existingArguments)} vs. {GetArgumentsText(arguments)}) and will not be redeclared, queue will be consumed as-is");
+        }
+
+
+        private static string GetArgumentsText(IRabbitMQArguments? arguments)
+        {
+            if (arguments == null || arguments.Count == 0)
+                return "empty";
+
             var argumentsText = new StringBuilder();
             foreach (var pair in arguments)
             {
@@ -60,9 +69,10 @@ namespace Tapeti.Tests.Mock
                 argumentsText.Append($"{pair.Key} = {pair.Value}");
             }
 
-            testOutputHelper.WriteLine($"Durable queue {queueName} exists with incompatible x-arguments ({argumentsText}) and will not be redeclared, queue will be consumed as-is");
+            return argumentsText.ToString();
         }
 
+
         public void QueueBind(string queueName, bool durable, string exchange, string routingKey)
         {
             testOutputHelper.WriteLine($"Binding {queueName} to exchange {exchange} with routing key {routingKey}");

Tapeti.Tests/Tapeti.Tests.csproj

@@ -2,6 +2,7 @@
 
   <PropertyGroup>
     <TargetFramework>net6.0</TargetFramework>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">

Tapeti.Transient/ITransientPublisher.cs

@@ -15,6 +15,6 @@ namespace Tapeti.Transient
         /// <param name="request"></param>
         /// <typeparam name="TRequest"></typeparam>
         /// <typeparam name="TResponse"></typeparam>
-        Task<TResponse> RequestResponse<TRequest, TResponse>(TRequest request);
+        Task<TResponse> RequestResponse<TRequest, TResponse>(TRequest request) where TRequest : class where TResponse : class;
     }
 }

Tapeti.Transient/Tapeti.Transient.csproj

@@ -12,6 +12,7 @@
     <PackageIcon>Tapeti.Flow.png</PackageIcon>
     <Version>2.0.0</Version>
     <LangVersion>9</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">

Tapeti.Transient/TransientExtension.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using Tapeti.Config;
 
 namespace Tapeti.Transient
@@ -31,7 +32,7 @@ namespace Tapeti.Transient
         /// <inheritdoc />
         public IEnumerable<object> GetMiddleware(IDependencyResolver dependencyResolver)
         {
-            return null;
+            return Enumerable.Empty<object>();
         }
 
 

Tapeti.Transient/TransientGenericBinding.cs

@@ -14,10 +14,10 @@ namespace Tapeti.Transient
         private readonly string dynamicQueuePrefix;
 
         /// <inheritdoc />
-        public string QueueName { get; private set; }
+        public string? QueueName { get; private set; }
 
         /// <inheritdoc />
-        public QueueType QueueType => QueueType.Dynamic;
+        public QueueType? QueueType => Config.QueueType.Dynamic;
 
 
         /// <summary>

Tapeti.Transient/TransientPublisher.cs

@@ -21,7 +21,7 @@ namespace Tapeti.Transient
 
 
         /// <inheritdoc />
-        public async Task<TResponse> RequestResponse<TRequest, TResponse>(TRequest request)
+        public async Task<TResponse> RequestResponse<TRequest, TResponse>(TRequest request) where TRequest : class where TResponse : class
         {
             return (TResponse)await router.RequestResponse(publisher, request);
         }

Tapeti.Transient/TransientRouter.cs

@@ -18,7 +18,7 @@ namespace Tapeti.Transient
         /// <summary>
         /// The generated name of the dynamic queue to which responses should be sent.
         /// </summary>
-        public string TransientResponseQueueName { get; set; }
+        public string? TransientResponseQueueName { get; set; }
 
 
         /// <summary>
@@ -41,7 +41,12 @@ namespace Tapeti.Transient
             if (!Guid.TryParse(context.Properties.CorrelationId, out var continuationID))
                 return;
 
-            if (map.TryRemove(continuationID, out var tcs))
+            if (!map.TryRemove(continuationID, out var tcs)) 
+                return;
+
+            if (context.Message == null)
+                throw new InvalidOperationException();
+
             tcs.TrySetResult(context.Message);
         }
 
@@ -72,7 +77,7 @@ namespace Tapeti.Transient
             {
                 // Simple cleanup of the task and map dictionary.
                 if (map.TryRemove(correlation, out tcs))
-                    tcs.TrySetResult(null);
+                    tcs.TrySetResult(null!);
 
                 throw;
             }
@@ -84,8 +89,10 @@ namespace Tapeti.Transient
         }
 
 
-        private void TimeoutResponse(object tcs)
+        private void TimeoutResponse(object? tcs)
         {
+            ArgumentNullException.ThrowIfNull(tcs, nameof(tcs));
+
             ((TaskCompletionSource<object>)tcs).TrySetException(new TimeoutException("Transient RequestResponse timed out at (ms) " + defaultTimeoutMs));
         }
     }

Tapeti/Config/ControllerMessageContextPayload.cs

@@ -8,7 +8,7 @@
         /// <summary>
         /// An instance of the controller referenced by the binding. Note: can be null during Cleanup or when bound to static methods.
         /// </summary>
-        public object Controller { get; }
+        public object? Controller { get; }
 
 
         /// <remarks>
@@ -22,7 +22,7 @@
         /// </summary>
         /// <param name="controller">An instance of the controller referenced by the binding</param>
         /// <param name="binding">The binding which is currently processing the message</param>
-        public ControllerMessageContextPayload(object controller, IControllerMethodBinding binding)
+        public ControllerMessageContextPayload(object? controller, IControllerMethodBinding binding)
         {
             Controller = controller;
             Binding = binding;

Tapeti/Config/IBinding.cs

@@ -29,13 +29,13 @@ namespace Tapeti.Config
         /// <summary>
         /// The name of the queue the binding is consuming. May change after a reconnect for dynamic queues.
         /// </summary>
-        string QueueName { get; }
+        string? QueueName { get; }
 
 
         /// <summary>
         /// Determines the type of queue the binding registers
         /// </summary>
-        QueueType QueueType { get; }
+        QueueType? QueueType { get; }
 
 
         /// <summary>
@@ -82,7 +82,7 @@ namespace Tapeti.Config
         /// <param name="messageClass">The message class to be bound to the queue</param>
         /// <param name="queueName">The name of the durable queue</param>
         /// <param name="arguments">Optional arguments</param>
-        ValueTask BindDurable(Type messageClass, string queueName, IRabbitMQArguments arguments);
+        ValueTask BindDurable(Type messageClass, string queueName, IRabbitMQArguments? arguments);
 
         /// <summary>
         /// Binds the messageClass to a dynamic auto-delete queue.
@@ -95,7 +95,7 @@ namespace Tapeti.Config
         /// <param name="queuePrefix">An optional prefix for the dynamic queue's name. If not provided, RabbitMQ's default logic will be used to create an amq.gen queue.</param>
         /// <param name="arguments">Optional arguments</param>
         /// <returns>The generated name of the dynamic queue</returns>
-        ValueTask<string> BindDynamic(Type messageClass, string queuePrefix, IRabbitMQArguments arguments);
+        ValueTask<string> BindDynamic(Type messageClass, string? queuePrefix, IRabbitMQArguments? arguments);
 
         /// <summary>
         /// Declares a durable queue but does not add a binding for a messageClass' routing key.
@@ -103,7 +103,7 @@ namespace Tapeti.Config
         /// </summary>
         /// <param name="queueName">The name of the durable queue</param>
         /// <param name="arguments">Optional arguments</param>
-        ValueTask BindDurableDirect(string queueName, IRabbitMQArguments arguments);
+        ValueTask BindDurableDirect(string queueName, IRabbitMQArguments? arguments);
 
         /// <summary>
         /// Declares a dynamic queue but does not add a binding for a messageClass' routing key.
@@ -113,7 +113,7 @@ namespace Tapeti.Config
         /// <param name="queuePrefix">An optional prefix for the dynamic queue's name. If not provided, RabbitMQ's default logic will be used to create an amq.gen queue.</param>
         /// <param name="arguments">Optional arguments</param>
         /// <returns>The generated name of the dynamic queue</returns>
-        ValueTask<string> BindDynamicDirect(Type messageClass, string queuePrefix, IRabbitMQArguments arguments);
+        ValueTask<string> BindDynamicDirect(Type messageClass, string? queuePrefix, IRabbitMQArguments? arguments);
 
         /// <summary>
         /// Declares a dynamic queue but does not add a binding for a messageClass' routing key.
@@ -122,7 +122,7 @@ namespace Tapeti.Config
         /// <param name="queuePrefix">An optional prefix for the dynamic queue's name. If not provided, RabbitMQ's default logic will be used to create an amq.gen queue.</param>
         /// <param name="arguments">Optional arguments</param>
         /// <returns>The generated name of the dynamic queue</returns>
-        ValueTask<string> BindDynamicDirect(string queuePrefix, IRabbitMQArguments arguments);
+        ValueTask<string> BindDynamicDirect(string? queuePrefix, IRabbitMQArguments? arguments);
 
         /// <summary>
         /// Marks the specified durable queue as having an obsolete binding. If after all bindings have subscribed, the queue only contains obsolete

Tapeti/Config/IControllerBindingContext.cs

@@ -11,7 +11,7 @@ namespace Tapeti.Config
     /// Injects a value for a controller method parameter.
     /// </summary>
     /// <param name="context"></param>
-    public delegate object ValueFactory(IMessageContext context);
+    public delegate object? ValueFactory(IMessageContext context);
 
 
     /// <summary>
@@ -19,7 +19,7 @@ namespace Tapeti.Config
     /// </summary>
     /// <param name="context"></param>
     /// <param name="value"></param>
-    public delegate ValueTask ResultHandler(IMessageContext context, object value);
+    public delegate ValueTask ResultHandler(IMessageContext context, object? value);
 
 
     /// <summary>
@@ -48,7 +48,7 @@ namespace Tapeti.Config
         /// The message class for this method. Can be null if not yet set by the default MessageBinding or other middleware.
         /// If required, call next first to ensure it is available.
         /// </summary>
-        Type MessageClass { get; }
+        Type? MessageClass { get; }
 
         /// <summary>
         /// Determines if SetMessageClass has already been called.

Tapeti/Config/IMessageContext.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 
 // ReSharper disable UnusedMemberInSuper.Global - public API
@@ -34,12 +35,12 @@ namespace Tapeti.Config
         /// <summary>
         /// Contains the raw body of the message.
         /// </summary>
-        byte[] RawBody { get; }
+        byte[]? RawBody { get; }
         
         /// <summary>
         /// Contains the decoded message instance.
         /// </summary>
-        object Message { get; }
+        object? Message { get; }
 
         /// <summary>
         /// Provides access to the message metadata.
@@ -87,7 +88,7 @@ namespace Tapeti.Config
         /// Returns true and the payload value if this message context was previously enriched with the payload T.
         /// </summary>
         /// <typeparam name="T">The payload type as passed to Enrich</typeparam>
-        bool TryGet<T>(out T payload) where T : IMessageContextPayload;
+        bool TryGet<T>([NotNullWhen(true)] out T? payload) where T : IMessageContextPayload;
 
         /// <summary>
         /// Stores a key-value pair in the context for passing information between the various
@@ -105,7 +106,7 @@ namespace Tapeti.Config
         /// <param name="value"></param>
         /// <returns>True if the value was found, False otherwise</returns>
         [Obsolete("For backwards compatibility only. Use Get<T> payload overload for typed properties instead")]
-        bool Get<T>(string key, out T value) where T : class;
+        bool Get<T>(string key, out T? value) where T : class;
     }
 
 

Tapeti/Config/IMessageProperties.cs

@@ -9,13 +9,13 @@ namespace Tapeti.Config
     public interface IMessageProperties
     {
         /// <summary></summary>
-        string ContentType { get; set; }
+        string? ContentType { get; set; }
 
         /// <summary></summary>
-        string CorrelationId { get; set; }
+        string? CorrelationId { get; set; }
 
         /// <summary></summary>
-        string ReplyTo { get; set; }
+        string? ReplyTo { get; set; }
 
         /// <summary></summary>
         bool? Persistent { get; set; }
@@ -37,7 +37,7 @@ namespace Tapeti.Config
         /// </summary>
         /// <param name="name"></param>
         /// <returns>The value if found, null otherwise</returns>
-        string GetHeader(string name);
+        string? GetHeader(string name);
 
 
         /// <summary>

Tapeti/Config/IPublishContext.cs

@@ -16,7 +16,7 @@ namespace Tapeti.Config
         /// <summary>
         /// The exchange to which the message will be published.
         /// </summary>
-        string Exchange { get; set; }
+        string? Exchange { get; set; }
 
         /// <summary>
         /// The routing key which will be included with the message.
@@ -31,6 +31,6 @@ namespace Tapeti.Config
         /// <summary>
         /// Provides access to the message metadata.
         /// </summary>
-        IMessageProperties Properties { get; }
+        IMessageProperties? Properties { get; }
     }
 }

Tapeti/Config/ITapetiConfig.cs

@@ -87,40 +87,13 @@ namespace Tapeti.Config
         /// </summary>
         /// <param name="method"></param>
         /// <returns>The binding if found, null otherwise</returns>
-        IControllerMethodBinding ForMethod(Delegate method);
+        IControllerMethodBinding? ForMethod(Delegate method);
 
         /// <summary>
         /// Searches for a binding linked to the specified method.
         /// </summary>
         /// <param name="method"></param>
         /// <returns>The binding if found, null otherwise</returns>
-        IControllerMethodBinding ForMethod(MethodInfo method);
+        IControllerMethodBinding? ForMethod(MethodInfo method);
     }
-
-
-    /*
-    public interface IBinding
-    {
-        Type Controller { get; }
-        MethodInfo Method { get; }
-        Type MessageClass { get; }
-        string QueueName { get; }
-        QueueBindingMode QueueBindingMode { get; set; }
-
-        IReadOnlyList<IMessageFilterMiddleware> MessageFilterMiddleware { get; }
-        IReadOnlyList<IMessageMiddleware> MessageMiddleware { get; }
-
-        bool Accept(Type messageClass);
-        bool Accept(IMessageContext context, object message);
-        Task Invoke(IMessageContext context, object message);
-    }
-    */
-
-
-    /*
-    public interface IBuildBinding : IBinding
-    {
-        void SetQueueName(string queueName);
-    }
-    */
 }

Tapeti/Connection/ITapetiClient.cs

@@ -37,9 +37,9 @@ namespace Tapeti.Connection
         }
 
         /// <inheritdoc />
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
-            if (ReferenceEquals(null, obj)) return false;
+            if (obj is null) return false;
             return obj is QueueBinding other && Equals(other);
         }
 
@@ -79,7 +79,7 @@ namespace Tapeti.Connection
         /// <param name="exchange">The exchange to publish the message to, or empty to send it directly to a queue</param>
         /// <param name="routingKey">The routing key for the message, or queue name if exchange is empty</param>
         /// <param name="mandatory">If true, an exception will be raised if the message can not be delivered to at least one queue</param>
-        Task Publish(byte[] body, IMessageProperties properties, string exchange, string routingKey, bool mandatory);
+        Task Publish(byte[] body, IMessageProperties properties, string? exchange, string routingKey, bool mandatory);
 
 
         /// <summary>
@@ -89,7 +89,7 @@ namespace Tapeti.Connection
         /// <param name="consumer">The consumer implementation which will receive the messages from the queue</param>
         /// <param name="cancellationToken">Cancelled when the connection is lost</param>
         /// <returns>The consumer tag as returned by BasicConsume.</returns>
-        Task<TapetiConsumerTag> Consume(string queueName, IConsumer consumer, CancellationToken cancellationToken);
+        Task<TapetiConsumerTag?> Consume(string queueName, IConsumer consumer, CancellationToken cancellationToken);
 
         /// <summary>
         /// Stops the consumer with the specified tag.
@@ -104,7 +104,7 @@ namespace Tapeti.Connection
         /// <param name="bindings">A list of bindings. Any bindings already on the queue which are not in this list will be removed</param>
         /// <param name="arguments">Optional arguments</param>
         /// <param name="cancellationToken">Cancelled when the connection is lost</param>
-        Task DurableQueueDeclare(string queueName, IEnumerable<QueueBinding> bindings, IRabbitMQArguments arguments, CancellationToken cancellationToken);
+        Task DurableQueueDeclare(string queueName, IEnumerable<QueueBinding> bindings, IRabbitMQArguments? arguments, CancellationToken cancellationToken);
 
         /// <summary>
         /// Verifies a durable queue exists. Will raise an exception if it does not.
@@ -112,7 +112,7 @@ namespace Tapeti.Connection
         /// <param name="queueName">The name of the queue to verify</param>
         /// <param name="arguments">Optional arguments</param>
         /// <param name="cancellationToken">Cancelled when the connection is lost</param>
-        Task DurableQueueVerify(string queueName, IRabbitMQArguments arguments, CancellationToken cancellationToken);
+        Task DurableQueueVerify(string queueName, IRabbitMQArguments? arguments, CancellationToken cancellationToken);
 
         /// <summary>
         /// Deletes a durable queue.
@@ -128,7 +128,7 @@ namespace Tapeti.Connection
         /// <param name="queuePrefix">An optional prefix for the dynamic queue's name. If not provided, RabbitMQ's default logic will be used to create an amq.gen queue.</param>
         /// <param name="arguments">Optional arguments</param>
         /// <param name="cancellationToken">Cancelled when the connection is lost</param>
-        Task<string> DynamicQueueDeclare(string queuePrefix, IRabbitMQArguments arguments, CancellationToken cancellationToken);
+        Task<string> DynamicQueueDeclare(string? queuePrefix, IRabbitMQArguments? arguments, CancellationToken cancellationToken);
 
         /// <summary>
         /// Add a binding to a dynamic queue.

Tapeti/Connection/RabbitMQArguments.cs

@@ -15,17 +15,10 @@ namespace Tapeti.Connection
         {
         }
 
-        #if NETSTANDARD2_1_OR_GREATER
+
         public RabbitMQArguments(IReadOnlyDictionary<string, object> values) : base(values)
         {
         }
-        #else
-        public RabbitMQArguments(IReadOnlyDictionary<string, object> values)
-        {
-            foreach (var pair in values)
-                Add(pair.Key, pair.Value);
-        }
-        #endif
 
 
         public void AddUTF8(string key, string value)

Tapeti/Connection/TapetiChannel.cs

@@ -21,7 +21,7 @@ namespace Tapeti.Connection
     {
         private readonly Func<IModel> modelFactory;
         private readonly object taskQueueLock = new();
-        private SingleThreadTaskQueue taskQueue;
+        private SingleThreadTaskQueue? taskQueue;
         private readonly ModelProvider modelProvider;
 
 
@@ -34,7 +34,7 @@ namespace Tapeti.Connection
 
         public async Task Reset()
         {
-            SingleThreadTaskQueue capturedTaskQueue;
+            SingleThreadTaskQueue? capturedTaskQueue;
             
             lock (taskQueueLock)
             {

Tapeti/Connection/TapetiClient.cs

@@ -43,7 +43,7 @@ namespace Tapeti.Connection
         /// <summary>
         /// Receives events when the connection state changes.
         /// </summary>
-        public IConnectionEventListener ConnectionEventListener { get; set; }
+        public IConnectionEventListener? ConnectionEventListener { get; set; }
 
 
         private readonly TapetiChannel consumeChannel;
@@ -53,9 +53,9 @@ namespace Tapeti.Connection
         // These fields must be locked using connectionLock
         private readonly object connectionLock = new();
         private long connectionReference;
-        private RabbitMQ.Client.IConnection connection;
+        private RabbitMQ.Client.IConnection? connection;
-        private IModel consumeChannelModel;
+        private IModel? consumeChannelModel;
-        private IModel publishChannelModel;
+        private IModel? publishChannelModel;
         private bool isClosing;
         private bool isReconnect;
         private DateTime connectedDateTime;
@@ -72,8 +72,15 @@ namespace Tapeti.Connection
 
         private class ConfirmMessageInfo
         {
-            public string ReturnKey;
+            public string ReturnKey { get; }
-            public TaskCompletionSource<int> CompletionSource;
+            public TaskCompletionSource<int> CompletionSource { get; }
+
+
+            public ConfirmMessageInfo(string returnKey, TaskCompletionSource<int> completionSource)
+            {
+                ReturnKey = returnKey;
+                CompletionSource = completionSource;
+            }
         }
 
 
@@ -110,7 +117,7 @@ namespace Tapeti.Connection
 
 
         /// <inheritdoc />
-        public async Task Publish(byte[] body, IMessageProperties properties, string exchange, string routingKey, bool mandatory)
+        public async Task Publish(byte[] body, IMessageProperties properties, string? exchange, string routingKey, bool mandatory)
         {
             if (string.IsNullOrEmpty(routingKey))
                 throw new ArgumentNullException(nameof(routingKey));
@@ -118,16 +125,13 @@ namespace Tapeti.Connection
 
             await GetTapetiChannel(TapetiChannelType.Publish).QueueWithProvider(async channelProvider =>
             {
-                Task<int> publishResultTask = null;
+                Task<int>? publishResultTask = null;
-                var messageInfo = new ConfirmMessageInfo
+                var messageInfo = new ConfirmMessageInfo(GetReturnKey(exchange ?? string.Empty, routingKey), new TaskCompletionSource<int>());
-                {
-                    ReturnKey = GetReturnKey(exchange, routingKey),
-                    CompletionSource = new TaskCompletionSource<int>()
-                };
 
 
                 channelProvider.WithRetryableChannel(channel =>
                 {
+                    if (exchange != null)
                         DeclareExchange(channel, exchange);
 
                     // The delivery tag is lost after a reconnect, register under the new tag
@@ -153,7 +157,7 @@ namespace Tapeti.Connection
                     try
                     {
                         var publishProperties = new RabbitMQMessageProperties(channel.CreateBasicProperties(), properties);
-                        channel.BasicPublish(exchange ?? "", routingKey, mandatory, publishProperties.BasicProperties, body);
+                        channel.BasicPublish(exchange ?? string.Empty, routingKey, mandatory, publishProperties.BasicProperties, body);
                     }
                     catch
                     {
@@ -202,7 +206,7 @@ namespace Tapeti.Connection
 
 
         /// <inheritdoc />
-        public async Task<TapetiConsumerTag> Consume(string queueName, IConsumer consumer, CancellationToken cancellationToken)
+        public async Task<TapetiConsumerTag?> Consume(string queueName, IConsumer consumer, CancellationToken cancellationToken)
         {
             if (deletedQueues.Contains(queueName))
                 return null;
@@ -212,7 +216,7 @@ namespace Tapeti.Connection
 
 
             long capturedConnectionReference = -1;
-            string consumerTag = null;
+            string? consumerTag = null;
 
             await GetTapetiChannel(TapetiChannelType.Consume).QueueRetryable(channel =>
             {
@@ -224,7 +228,9 @@ namespace Tapeti.Connection
                 consumerTag = channel.BasicConsume(queueName, false, basicConsumer);
             });
 
-            return new TapetiConsumerTag(capturedConnectionReference, consumerTag);
+            return consumerTag == null 
+                ? null 
+                : new TapetiConsumerTag(capturedConnectionReference, consumerTag);
         }
 
 
@@ -289,7 +295,7 @@ namespace Tapeti.Connection
         }
 
 
-        private async Task<bool> GetDurableQueueDeclareRequired(string queueName, IRabbitMQArguments arguments)
+        private async Task<bool> GetDurableQueueDeclareRequired(string queueName, IRabbitMQArguments? arguments)
         {
             var existingQueue = await GetQueueInfo(queueName);
             if (existingQueue == null) 
@@ -298,9 +304,6 @@ namespace Tapeti.Connection
             if (!existingQueue.Durable || existingQueue.AutoDelete || existingQueue.Exclusive)
                 throw new InvalidOperationException($"Durable queue {queueName} already exists with incompatible parameters, durable = {existingQueue.Durable} (expected True), autoDelete = {existingQueue.AutoDelete} (expected False), exclusive = {existingQueue.Exclusive} (expected False)");
 
-            if (arguments == null && existingQueue.Arguments.Count == 0)
-                return true;
-
             var existingArguments = ConvertJsonArguments(existingQueue.Arguments);
             if (existingArguments.NullSafeSameValues(arguments))
                 return true;
@@ -310,7 +313,7 @@ namespace Tapeti.Connection
         }
 
 
-        private static RabbitMQArguments ConvertJsonArguments(IReadOnlyDictionary<string, JObject> arguments)
+        private static RabbitMQArguments? ConvertJsonArguments(IReadOnlyDictionary<string, JObject>? arguments)
         {
             if (arguments == null)
                 return null;
@@ -325,7 +328,6 @@ namespace Tapeti.Connection
                     JTokenType.Float => pair.Value.Value<double>(),
                     JTokenType.String => Encoding.UTF8.GetBytes(pair.Value.Value<string>() ?? string.Empty),
                     JTokenType.Boolean => pair.Value.Value<bool>(),
-                    JTokenType.Null => null,
                     _ => throw new ArgumentOutOfRangeException(nameof(arguments))
                 };
 
@@ -338,7 +340,7 @@ namespace Tapeti.Connection
 
 
         /// <inheritdoc />
-        public async Task DurableQueueDeclare(string queueName, IEnumerable<QueueBinding> bindings, IRabbitMQArguments arguments, CancellationToken cancellationToken)
+        public async Task DurableQueueDeclare(string queueName, IEnumerable<QueueBinding> bindings, IRabbitMQArguments? arguments, CancellationToken cancellationToken)
         {
             var declareRequired = await GetDurableQueueDeclareRequired(queueName, arguments);
 
@@ -373,7 +375,7 @@ namespace Tapeti.Connection
         }
 
 
-        private static IDictionary<string, object> GetDeclareArguments(IRabbitMQArguments arguments)
+        private static IDictionary<string, object>? GetDeclareArguments(IRabbitMQArguments? arguments)
         {
             return arguments == null || arguments.Count == 0 
                 ? null 
@@ -382,7 +384,7 @@ namespace Tapeti.Connection
 
 
         /// <inheritdoc />
-        public async Task DurableQueueVerify(string queueName, IRabbitMQArguments arguments, CancellationToken cancellationToken)
+        public async Task DurableQueueVerify(string queueName, IRabbitMQArguments? arguments, CancellationToken cancellationToken)
         {
             if (!await GetDurableQueueDeclareRequired(queueName, arguments))
                 return;
@@ -484,9 +486,9 @@ namespace Tapeti.Connection
 
 
         /// <inheritdoc />
-        public async Task<string> DynamicQueueDeclare(string queuePrefix, IRabbitMQArguments arguments, CancellationToken cancellationToken)
+        public async Task<string> DynamicQueueDeclare(string? queuePrefix, IRabbitMQArguments? arguments, CancellationToken cancellationToken)
         {
-            string queueName = null;
+            string? queueName = null;
             var bindingLogger = logger as IBindingLogger;
 
             await GetTapetiChannel(TapetiChannelType.Consume).Queue(channel =>
@@ -507,6 +509,10 @@ namespace Tapeti.Connection
                 }
             });
 
+            cancellationToken.ThrowIfCancellationRequested();
+            if (queueName == null)
+                throw new InvalidOperationException("Failed to declare dynamic queue");
+
             return queueName;
         }
 
@@ -528,9 +534,9 @@ namespace Tapeti.Connection
         /// <inheritdoc />
         public async Task Close()
         {
-            IModel capturedConsumeModel;
+            IModel? capturedConsumeModel;
-            IModel capturedPublishModel;
+            IModel? capturedPublishModel;
-            RabbitMQ.Client.IConnection capturedConnection;
+            RabbitMQ.Client.IConnection? capturedConnection;
 
             lock (connectionLock)
             {
@@ -578,10 +584,10 @@ namespace Tapeti.Connection
         private class ManagementQueueInfo
         {
             [JsonProperty("name")]
-            public string Name { get; set; }
+            public string? Name { get; set; }
 
             [JsonProperty("vhost")]
-            public string VHost { get; set; }
+            public string? VHost { get; set; }
 
             [JsonProperty("durable")]
             public bool Durable { get; set; }
@@ -593,7 +599,7 @@ namespace Tapeti.Connection
             public bool Exclusive { get; set; }
 
             [JsonProperty("arguments")]
-            public Dictionary<string, JObject> Arguments { get; set; }
+            public Dictionary<string, JObject>? Arguments { get; set; }
 
             [JsonProperty("messages")]
             public uint Messages { get; set; }
@@ -601,7 +607,7 @@ namespace Tapeti.Connection
 
 
 
-        private async Task<ManagementQueueInfo> GetQueueInfo(string queueName)
+        private async Task<ManagementQueueInfo?> GetQueueInfo(string queueName)
         {
             var virtualHostPath = Uri.EscapeDataString(connectionParams.VirtualHost);
             var queuePath = Uri.EscapeDataString(queueName);
@@ -622,25 +628,25 @@ namespace Tapeti.Connection
         private class ManagementBinding
         {
             [JsonProperty("source")]
-            public string Source { get; set; }
+            public string? Source { get; set; }
 
             [JsonProperty("vhost")]
-            public string Vhost { get; set; }
+            public string? Vhost { get; set; }
 
             [JsonProperty("destination")]
-            public string Destination { get; set; }
+            public string? Destination { get; set; }
 
             [JsonProperty("destination_type")]
-            public string DestinationType { get; set; }
+            public string? DestinationType { get; set; }
 
             [JsonProperty("routing_key")]
-            public string RoutingKey { get; set; }
+            public string? RoutingKey { get; set; }
 
             [JsonProperty("arguments")]
-            public Dictionary<string, string> Arguments { get; set; }
+            public Dictionary<string, string>? Arguments { get; set; }
 
             [JsonProperty("properties_key")]
-            public string PropertiesKey { get; set; }
+            public string? PropertiesKey { get; set; }
         }
 
         
@@ -658,8 +664,8 @@ namespace Tapeti.Connection
 
                 // Filter out the binding to an empty source, which is always present for direct-to-queue routing
                 return bindings?
-                    .Where(binding => !string.IsNullOrEmpty(binding.Source))
+                    .Where(binding => !string.IsNullOrEmpty(binding.Source) && !string.IsNullOrEmpty(binding.RoutingKey))
-                    .Select(binding => new QueueBinding(binding.Source, binding.RoutingKey)) 
+                    .Select(binding => new QueueBinding(binding.Source!, binding.RoutingKey!)) 
                        ?? Enumerable.Empty<QueueBinding>();
             });
         }
@@ -723,9 +729,6 @@ namespace Tapeti.Connection
 
         private void DeclareExchange(IModel channel, string exchange)
         {
-            if (string.IsNullOrEmpty(exchange))
-                return;
-
             if (declaredExchanges.Contains(exchange))
                 return;
 
@@ -791,9 +794,9 @@ namespace Tapeti.Connection
             {
                 try
                 {
-                    RabbitMQ.Client.IConnection capturedConnection;
+                    RabbitMQ.Client.IConnection? capturedConnection;
-                    IModel capturedConsumeChannelModel;
+                    IModel? capturedConsumeChannelModel;
-                    IModel capturedPublishChannelModel;
+                    IModel? capturedPublishChannelModel;
 
 
                     lock (connectionLock)
@@ -805,7 +808,7 @@ namespace Tapeti.Connection
                     {
                         try
                         {
-                            if (connection.IsOpen)
+                            if (connection is { IsOpen: true })
                                 connection.Close();
                         }
                         catch (AlreadyClosedException)
@@ -813,7 +816,7 @@ namespace Tapeti.Connection
                         }
                         finally
                         {
-                            connection.Dispose();
+                            connection?.Dispose();
                         }
 
                         connection = null;
@@ -873,12 +876,7 @@ namespace Tapeti.Connection
                             consumeChannelModel = null;
                         }
 
-                        ConnectionEventListener?.Disconnected(new DisconnectedEventArgs
+                        ConnectionEventListener?.Disconnected(new DisconnectedEventArgs(e.ReplyCode, e.ReplyText));
-                        {
-                            ReplyCode = e.ReplyCode,
-                            ReplyText = e.ReplyText
-                        });
-
                         logger.Disconnect(new DisconnectContext(connectionParams, e.ReplyCode, e.ReplyText));
 
                         // Reconnect if the disconnect was unexpected
@@ -906,11 +904,7 @@ namespace Tapeti.Connection
 
                     connectedDateTime = DateTime.UtcNow;
 
-                    var connectedEventArgs = new ConnectedEventArgs
+                    var connectedEventArgs = new ConnectedEventArgs(connectionParams, capturedConnection.LocalPort);
-                    {
-                        ConnectionParams = connectionParams,
-                        LocalPort = capturedConnection.LocalPort
-                    };
 
                     if (isReconnect)
                         ConnectionEventListener?.Reconnected(connectedEventArgs);
@@ -938,7 +932,7 @@ namespace Tapeti.Connection
         }
 
 
-        private void HandleBasicReturn(object sender, BasicReturnEventArgs e)        
+        private void HandleBasicReturn(object? sender, BasicReturnEventArgs e)        
         {
             /*
              * "If the message is also published as mandatory, the basic.return is sent to the client before basic.ack."
@@ -968,7 +962,7 @@ namespace Tapeti.Connection
         }
 
 
-        private void HandleBasicAck(object sender, BasicAckEventArgs e)
+        private void HandleBasicAck(object? sender, BasicAckEventArgs e)
         {
             Monitor.Enter(confirmLock);
             try
@@ -999,7 +993,7 @@ namespace Tapeti.Connection
         }
 
 
-        private void HandleBasicNack(object sender, BasicNackEventArgs e)
+        private void HandleBasicNack(object? sender, BasicNackEventArgs e)
         {
             Monitor.Enter(confirmLock);
             try
@@ -1048,10 +1042,10 @@ namespace Tapeti.Connection
             public TapetiConnectionParams ConnectionParams { get; }
             public bool IsReconnect { get; }
             public int LocalPort { get; }
-            public Exception Exception { get; }
+            public Exception? Exception { get; }
 
 
-            public ConnectContext(TapetiConnectionParams connectionParams, bool isReconnect, int localPort = 0, Exception exception = null)
+            public ConnectContext(TapetiConnectionParams connectionParams, bool isReconnect, int localPort = 0, Exception? exception = null)
             {
                 ConnectionParams = connectionParams;
                 IsReconnect = isReconnect;

Tapeti/Connection/TapetiConsumer.cs

@@ -40,7 +40,7 @@ namespace Tapeti.Connection
         /// <inheritdoc />
         public async Task<ConsumeResult> Consume(string exchange, string routingKey, IMessageProperties properties, byte[] body)
         {
-            object message = null;
+            object? message = null;
             try
             {
                 try
@@ -73,7 +73,7 @@ namespace Tapeti.Connection
                     RawBody = body,
                     Message = message,
                     Properties = properties,
-                    Binding = null,
+                    Binding = new ExceptionContextBinding(queueName),
                     ConnectionClosed = CancellationToken.None
                 };
                 
@@ -184,5 +184,42 @@ namespace Tapeti.Connection
             public string RoutingKey;
             public IMessageProperties Properties;
         }
+
+
+        private class ExceptionContextBinding : IBinding
+        {
+            public string? QueueName { get; }
+            public QueueType? QueueType => null;
+
+
+            public ExceptionContextBinding(string? queueName)
+            {
+                QueueName = queueName;
+            }
+
+
+            public ValueTask Apply(IBindingTarget target)
+            {
+                throw new InvalidOperationException("Apply method should not be called on a binding in an Exception context");
+            }
+
+
+            public bool Accept(Type messageClass)
+            {
+                throw new InvalidOperationException("Accept method should not be called on a binding in an Exception context");
+            }
+
+
+            public ValueTask Invoke(IMessageContext context)
+            {
+                throw new InvalidOperationException("Invoke method should not be called on a binding in an Exception context");
+            }
+
+
+            public ValueTask Cleanup(IMessageContext context, ConsumeResult consumeResult)
+            {
+                throw new InvalidOperationException("Cleanup method should not be called on a binding in an Exception context");
+            }
+        }
     }
 }

Tapeti/Connection/TapetiPublisher.cs

@@ -38,14 +38,14 @@ namespace Tapeti.Connection
 
 
         /// <inheritdoc />
-        public async Task PublishRequest<TController, TRequest, TResponse>(TRequest message, Expression<Func<TController, Action<TResponse>>> responseMethodSelector) where TController : class
+        public async Task PublishRequest<TController, TRequest, TResponse>(TRequest message, Expression<Func<TController, Action<TResponse>>> responseMethodSelector) where TController : class where TRequest : class where TResponse : class
         {
             await PublishRequest(message, responseMethodSelector.Body);
         }
 
 
         /// <inheritdoc />
-        public async Task PublishRequest<TController, TRequest, TResponse>(TRequest message, Expression<Func<TController, Func<TResponse, Task>>> responseMethodSelector) where TController : class
+        public async Task PublishRequest<TController, TRequest, TResponse>(TRequest message, Expression<Func<TController, Func<TResponse, Task>>> responseMethodSelector) where TController : class where TRequest : class where TResponse : class
         {
             await PublishRequest(message, responseMethodSelector.Body);
         }
@@ -97,7 +97,7 @@ namespace Tapeti.Connection
 
 
         /// <inheritdoc />
-        public async Task Publish(object message, IMessageProperties properties, bool mandatory)
+        public async Task Publish(object message, IMessageProperties? properties, bool mandatory)
         {
             var messageClass = message.GetType();
             var exchange = exchangeStrategy.GetExchange(messageClass);
@@ -108,13 +108,13 @@ namespace Tapeti.Connection
 
 
         /// <inheritdoc />
-        public async Task PublishDirect(object message, string queueName, IMessageProperties properties, bool mandatory)
+        public async Task PublishDirect(object message, string queueName, IMessageProperties? properties, bool mandatory)
         {
             await Publish(message, properties, null, queueName, mandatory);
         }
 
 
-        private async Task Publish(object message, IMessageProperties properties, string exchange, string routingKey, bool mandatory)
+        private async Task Publish(object message, IMessageProperties? properties, string? exchange, string routingKey, bool mandatory)
         {
             var writableProperties = new MessageProperties(properties);
 
@@ -151,11 +151,11 @@ namespace Tapeti.Connection
 
         private class PublishContext : IPublishContext
         {
-            public ITapetiConfig Config { get; init; }
+            public ITapetiConfig Config { get; init; } = null!;
-            public string Exchange { get; set; }
+            public string? Exchange { get; set; }
-            public string RoutingKey { get; init; }
+            public string RoutingKey { get; init; } = null!;
-            public object Message { get; init; }
+            public object Message { get; init; } = null!;
-            public IMessageProperties Properties { get; init; }
+            public IMessageProperties? Properties { get; init; }
         }
     }
 }

Tapeti/Connection/TapetiSubscriber.cs

@@ -16,7 +16,7 @@ namespace Tapeti.Connection
         private bool consuming;
         private readonly List<TapetiConsumerTag> consumerTags = new();
 
-        private CancellationTokenSource initializeCancellationTokenSource;
+        private CancellationTokenSource? initializeCancellationTokenSource;
 
 
         public TapetiSubscriber(Func<ITapetiClient> clientFactory, ITapetiConfig config)
@@ -141,15 +141,24 @@ namespace Tapeti.Connection
 
         private async Task ConsumeQueues(CancellationToken cancellationToken)
         {
-            var queues = config.Bindings.GroupBy(binding => binding.QueueName);
+            var queues = config.Bindings.GroupBy(binding =>
+            {
+                if (string.IsNullOrEmpty(binding.QueueName))
+                    throw new InvalidOperationException("QueueName must not be empty");
 
-            consumerTags.AddRange((await Task.WhenAll(queues.Select(async group =>
+                return binding.QueueName;
+            });
+
+            consumerTags.AddRange(
+                (await Task.WhenAll(queues.Select(async group =>
                 {
                     var queueName = group.Key;
                     var consumer = new TapetiConsumer(cancellationToken, config, queueName, group);
 
                     return await clientFactory().Consume(queueName, consumer, cancellationToken);
-            }))).Where(t => t != null));
+                })))
+                .Where(t => t?.ConsumerTag != null)
+                .Cast<TapetiConsumerTag>());
         }
 
 
@@ -164,7 +173,7 @@ namespace Tapeti.Connection
             {
                 public string QueueName;
                 public List<Type> MessageClasses;
-                public IRabbitMQArguments Arguments;
+                public IRabbitMQArguments? Arguments;
             }
 
             private readonly Dictionary<string, List<DynamicQueueInfo>> dynamicQueues = new();
@@ -185,12 +194,12 @@ namespace Tapeti.Connection
             }
 
 
-            public abstract ValueTask BindDurable(Type messageClass, string queueName, IRabbitMQArguments arguments);
+            public abstract ValueTask BindDurable(Type messageClass, string queueName, IRabbitMQArguments? arguments);
-            public abstract ValueTask BindDurableDirect(string queueName, IRabbitMQArguments arguments);
+            public abstract ValueTask BindDurableDirect(string queueName, IRabbitMQArguments? arguments);
             public abstract ValueTask BindDurableObsolete(string queueName);
 
 
-            public async ValueTask<string> BindDynamic(Type messageClass, string queuePrefix, IRabbitMQArguments arguments)
+            public async ValueTask<string> BindDynamic(Type messageClass, string? queuePrefix, IRabbitMQArguments? arguments)
             {
                 var result = await DeclareDynamicQueue(messageClass, queuePrefix, arguments);
                 if (!result.IsNewMessageClass) 
@@ -205,14 +214,14 @@ namespace Tapeti.Connection
             }
 
 
-            public async ValueTask<string> BindDynamicDirect(Type messageClass, string queuePrefix, IRabbitMQArguments arguments)
+            public async ValueTask<string> BindDynamicDirect(Type messageClass, string? queuePrefix, IRabbitMQArguments? arguments)
             {
                 var result = await DeclareDynamicQueue(messageClass, queuePrefix, arguments);
                 return result.QueueName;
             }
 
 
-            public async ValueTask<string> BindDynamicDirect(string queuePrefix, IRabbitMQArguments arguments)
+            public async ValueTask<string> BindDynamicDirect(string? queuePrefix, IRabbitMQArguments? arguments)
             {
                 // If we don't know the routing key, always create a new queue to ensure there is no overlap.
                 // Keep it out of the dynamicQueues dictionary, so it can't be re-used later on either.
@@ -226,7 +235,7 @@ namespace Tapeti.Connection
                 public bool IsNewMessageClass;
             }
 
-            private async Task<DeclareDynamicQueueResult> DeclareDynamicQueue(Type messageClass, string queuePrefix, IRabbitMQArguments arguments)
+            private async Task<DeclareDynamicQueueResult> DeclareDynamicQueue(Type messageClass, string? queuePrefix, IRabbitMQArguments? arguments)
             {
                 // Group by prefix
                 var key = queuePrefix ?? "";
@@ -282,7 +291,7 @@ namespace Tapeti.Connection
             private struct DurableQueueInfo
             {
                 public List<Type> MessageClasses;
-                public IRabbitMQArguments Arguments;
+                public IRabbitMQArguments? Arguments;
             }
 
 
@@ -295,7 +304,7 @@ namespace Tapeti.Connection
             }
 
 
-            public override ValueTask BindDurable(Type messageClass, string queueName, IRabbitMQArguments arguments)
+            public override ValueTask BindDurable(Type messageClass, string queueName, IRabbitMQArguments? arguments)
             {
                 // Collect the message classes per queue so we can determine afterwards
                 // if any of the bindings currently set on the durable queue are no
@@ -324,7 +333,7 @@ namespace Tapeti.Connection
         }
 
 
-            public override ValueTask BindDurableDirect(string queueName, IRabbitMQArguments arguments)
+            public override ValueTask BindDurableDirect(string queueName, IRabbitMQArguments? arguments)
             {
                 if (!durableQueues.TryGetValue(queueName, out var durableQueueInfo))
                 {
@@ -396,12 +405,12 @@ namespace Tapeti.Connection
             }
 
 
-            public override async ValueTask BindDurable(Type messageClass, string queueName, IRabbitMQArguments arguments)
+            public override async ValueTask BindDurable(Type messageClass, string queueName, IRabbitMQArguments? arguments)
             {
                 await VerifyDurableQueue(queueName, arguments);
             }
 
-            public override async ValueTask BindDurableDirect(string queueName, IRabbitMQArguments arguments)
+            public override async ValueTask BindDurableDirect(string queueName, IRabbitMQArguments? arguments)
             {
                 await VerifyDurableQueue(queueName, arguments);
             }
@@ -412,7 +421,7 @@ namespace Tapeti.Connection
             }
 
 
-            private async Task VerifyDurableQueue(string queueName, IRabbitMQArguments arguments)
+            private async Task VerifyDurableQueue(string queueName, IRabbitMQArguments? arguments)
             {
                 if (!durableQueues.Add(queueName))
                     return;
@@ -429,12 +438,12 @@ namespace Tapeti.Connection
             }
 
 
-            public override ValueTask BindDurable(Type messageClass, string queueName, IRabbitMQArguments arguments)
+            public override ValueTask BindDurable(Type messageClass, string queueName, IRabbitMQArguments? arguments)
             {
                 return default;
             }
 
-            public override ValueTask BindDurableDirect(string queueName, IRabbitMQArguments arguments)
+            public override ValueTask BindDurableDirect(string queueName, IRabbitMQArguments? arguments)
             {
                 return default;
             }

Tapeti/Default/ConsoleLogger.cs

@@ -80,14 +80,17 @@ namespace Tapeti.Default
         }
 
         /// <inheritdoc />
-        public void QueueExistsWarning(string queueName, IRabbitMQArguments existingArguments, IRabbitMQArguments arguments)
+        public void QueueExistsWarning(string queueName, IRabbitMQArguments? existingArguments, IRabbitMQArguments? arguments)
         {
             Console.WriteLine($"[Tapeti] Durable queue {queueName} exists with incompatible x-arguments ({GetArgumentsText(existingArguments)} vs. {GetArgumentsText(arguments)}) and will not be redeclared, queue will be consumed as-is");
         }
 
 
-        private static string GetArgumentsText(IRabbitMQArguments arguments)
+        private static string GetArgumentsText(IRabbitMQArguments? arguments)
         {
+            if (arguments == null || arguments.Count == 0)
+                return "empty";
+
             var argumentsText = new StringBuilder();
             foreach (var pair in arguments)
             {

Tapeti/Default/ControllerBindingContext.cs

@@ -26,7 +26,7 @@ namespace Tapeti.Default
 
 
         /// <inheritdoc />
-        public Type MessageClass { get; set; }
+        public Type? MessageClass { get; set; }
 
         /// <inheritdoc />
         public bool HasMessageClass => MessageClass != null;
@@ -44,10 +44,12 @@ namespace Tapeti.Default
         public IBindingResult Result => result;
 
 
-        public ControllerBindingContext(IEnumerable<ParameterInfo> parameters, ParameterInfo result)
+        public ControllerBindingContext(Type controller, MethodInfo method, IEnumerable<ParameterInfo> parameters, ParameterInfo result)
         {
-            this.parameters = parameters.Select(parameter => new ControllerBindingParameter(parameter)).ToList();
+            Controller = controller;
+            Method = method;
 
+            this.parameters = parameters.Select(parameter => new ControllerBindingParameter(parameter)).ToList();
             this.result = new ControllerBindingResult(result);
         }
 
@@ -84,7 +86,13 @@ namespace Tapeti.Default
         /// </summary>
         public IEnumerable<ValueFactory> GetParameterHandlers()
         {
-            return parameters.Select(p => p.Binding);
+            return parameters.Select(p =>
+            {
+                if (p.Binding == null)
+                    throw new TopologyConfigurationException($"No Binding for parameter {p.Info.Name}");
+
+                return p.Binding;
+            });
         }
 
 
@@ -92,7 +100,7 @@ namespace Tapeti.Default
         /// Returns the configured result handler.
         /// </summary>
         /// <returns></returns>
-        public ResultHandler GetResultHandler()
+        public ResultHandler? GetResultHandler()
         {
             return result.Handler;
         }
@@ -107,7 +115,7 @@ namespace Tapeti.Default
         /// <summary>
         /// Provides access to the configured binding.
         /// </summary>
-        public ValueFactory Binding { get; set; }
+        public ValueFactory? Binding { get; set; }
 
 
         /// <inheritdoc />
@@ -146,7 +154,7 @@ namespace Tapeti.Default
         /// <summary>
         /// Provides access to the configured handler.
         /// </summary>
-        public ResultHandler Handler { get; set; }
+        public ResultHandler? Handler { get; set; }
 
 
         /// <inheritdoc />

Tapeti/Default/ControllerMethodBinding.cs

@@ -60,7 +60,7 @@ namespace Tapeti.Default
             /// <summary>
             /// The return value handler.
             /// </summary>
-            public ResultHandler ResultHandler;
+            public ResultHandler? ResultHandler;
 
 
             /// <summary>
@@ -87,10 +87,10 @@ namespace Tapeti.Default
 
 
         /// <inheritdoc />
-        public string QueueName { get; private set; }
+        public string? QueueName { get; private set; }
 
         /// <inheritdoc />
-        public QueueType QueueType => bindingInfo.QueueInfo.QueueType;
+        public QueueType? QueueType => bindingInfo.QueueInfo.QueueType;
 
         /// <inheritdoc />
         public Type Controller => bindingInfo.ControllerType;
@@ -116,7 +116,7 @@ namespace Tapeti.Default
                 switch (bindingInfo.BindingTargetMode)
                 {
                     case BindingTargetMode.Default:
-                        if (bindingInfo.QueueInfo.QueueType == QueueType.Dynamic)
+                        if (bindingInfo.QueueInfo.QueueType == Config.QueueType.Dynamic)
                             QueueName = await target.BindDynamic(bindingInfo.MessageClass, bindingInfo.QueueInfo.Name, bindingInfo.QueueInfo.QueueArguments);
                         else
                         {
@@ -127,7 +127,7 @@ namespace Tapeti.Default
                         break;
 
                     case BindingTargetMode.Direct:
-                        if (bindingInfo.QueueInfo.QueueType == QueueType.Dynamic)
+                        if (bindingInfo.QueueInfo.QueueType == Config.QueueType.Dynamic)
                             QueueName = await target.BindDynamicDirect(bindingInfo.MessageClass, bindingInfo.QueueInfo.Name, bindingInfo.QueueInfo.QueueArguments);
                         else
                         {
@@ -141,7 +141,7 @@ namespace Tapeti.Default
                         throw new ArgumentOutOfRangeException(nameof(bindingInfo.BindingTargetMode), bindingInfo.BindingTargetMode, "Invalid BindingTargetMode");
                 }
             }
-            else if (bindingInfo.QueueInfo.QueueType == QueueType.Durable)
+            else if (bindingInfo.QueueInfo.QueueType == Config.QueueType.Durable)
             {
                 await target.BindDurableObsolete(bindingInfo.QueueInfo.Name);
                 QueueName = bindingInfo.QueueInfo.Name;
@@ -159,8 +159,11 @@ namespace Tapeti.Default
         /// <inheritdoc />
         public async ValueTask Invoke(IMessageContext context)
         {
+            if (context.Binding == null)
+                throw new InvalidOperationException("Invoke should not be called on a context without a binding");
+
             var controller = Method.IsStatic ? null : dependencyResolver.Resolve(bindingInfo.ControllerType);
-            context.Store(new ControllerMessageContextPayload(controller, context.Binding as IControllerMethodBinding));
+            context.Store(new ControllerMessageContextPayload(controller, (IControllerMethodBinding)context.Binding));
             
             if (!await FilterAllowed(context))
                 return;
@@ -202,7 +205,7 @@ namespace Tapeti.Default
         private delegate ValueTask MessageHandlerFunc(IMessageContext context);
 
 
-        private MessageHandlerFunc WrapMethod(MethodInfo method, IEnumerable<ValueFactory> parameterFactories, ResultHandler resultHandler)
+        private MessageHandlerFunc WrapMethod(MethodInfo method, IEnumerable<ValueFactory> parameterFactories, ResultHandler? resultHandler)
         {
             if (resultHandler != null)
                 return WrapResultHandlerMethod(method.CreateExpressionInvoke(), parameterFactories, resultHandler);
@@ -296,8 +299,8 @@ namespace Tapeti.Default
 
         private void AddExceptionData(Exception exception)
         {
-            exception.Data["Tapeti.Controller.Name"] = bindingInfo.ControllerType?.FullName;
+            exception.Data["Tapeti.Controller.Name"] = bindingInfo.ControllerType.FullName;
-            exception.Data["Tapeti.Controller.Method"] = bindingInfo.Method?.Name;
+            exception.Data["Tapeti.Controller.Method"] = bindingInfo.Method.Name;
         }
 
 
@@ -319,12 +322,19 @@ namespace Tapeti.Default
             /// <summary>
             /// Optional arguments (x-arguments) passed when declaring the queue.
             /// </summary>
-            public IRabbitMQArguments QueueArguments { get; set; }
+            public IRabbitMQArguments? QueueArguments { get; set; }
                 
             /// <summary>
             /// Determines if the QueueInfo properties contain a valid combination.
             /// </summary>
             public bool IsValid => QueueType == QueueType.Dynamic || !string.IsNullOrEmpty(Name);
+
+
+            public QueueInfo(QueueType queueType, string name)
+            {
+                QueueType = queueType;
+                Name = name;
+            }
         }
     }
 }

Tapeti/Default/FallbackStringEnumConverter.cs

@@ -24,7 +24,7 @@ namespace Tapeti.Default
 
 
         /// <inheritdoc />
-        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        public override void WriteJson(JsonWriter writer, object? value, JsonSerializer serializer)
         {
             if (value == null)
             {
@@ -41,7 +41,7 @@ namespace Tapeti.Default
 
 
         /// <inheritdoc />
-        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        public override object? ReadJson(JsonReader reader, Type objectType, object? existingValue, JsonSerializer serializer)
         {
             var isNullable = IsNullableType(objectType);
 

Tapeti/Default/JsonMessageSerializer.cs

@@ -46,7 +46,7 @@ namespace Tapeti.Default
 
 
         /// <inheritdoc />
-        public object Deserialize(byte[] body, IMessageProperties properties)
+        public object? Deserialize(byte[] body, IMessageProperties properties)
         {
             if (properties.ContentType is not ContentType)
                 throw new ArgumentException($"content_type must be {ContentType}");

Tapeti/Default/MessageContext.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 using System.Threading.Tasks;
 using Tapeti.Config;
@@ -12,28 +13,28 @@ namespace Tapeti.Default
 
 
         /// <inheritdoc />
-        public ITapetiConfig Config { get; set; }
+        public ITapetiConfig Config { get; set; } = null!;
 
         /// <inheritdoc />
-        public string Queue { get; set; }
+        public string Queue { get; set; } = null!;
 
         /// <inheritdoc />
-        public string Exchange { get; set; }
+        public string Exchange { get; set; } = null!;
 
         /// <inheritdoc />
-        public string RoutingKey { get; set; }
+        public string RoutingKey { get; set; } = null!;
 
         /// <inheritdoc />
-        public byte[] RawBody { get; set; }
+        public byte[] RawBody { get; set; } = null!;
 
         /// <inheritdoc />
-        public object Message { get; set; }
+        public object? Message { get; set; }
 
         /// <inheritdoc />
-        public IMessageProperties Properties { get; set; }
+        public IMessageProperties Properties { get; set; } = null!;
 
         /// <inheritdoc />
-        public IBinding Binding { get; set; }
+        public IBinding Binding { get; set; } = null!;
 
         /// <inheritdoc />
         public CancellationToken ConnectionClosed { get; set; }
@@ -57,7 +58,7 @@ namespace Tapeti.Default
             return (T)payloads[typeof(T)];
         }
 
-        public bool TryGet<T>(out T payload) where T : IMessageContextPayload
+        public bool TryGet<T>([NotNullWhen(true)] out T? payload) where T : IMessageContextPayload
         {
             if (payloads.TryGetValue(typeof(T), out var payloadValue))
             {
@@ -100,7 +101,7 @@ namespace Tapeti.Default
 
 
         /// <inheritdoc />
-        public bool Get<T>(string key, out T value) where T : class
+        public bool Get<T>(string key, out T? value) where T : class
         {
             if (!TryGet<KeyValuePayload>(out var payload) ||
                 !payload.TryGetValue(key, out var objectValue))
@@ -109,7 +110,7 @@ namespace Tapeti.Default
                 return false;
             }
 
-            value = (T)objectValue;
+            value = (T?)objectValue;
             return true;
         }
 
@@ -132,7 +133,7 @@ namespace Tapeti.Default
             }
 
 
-            public bool TryGetValue(string key, out object value)
+            public bool TryGetValue(string key, out object? value)
             {
                 return items.TryGetValue(key, out value);
             }

Tapeti/Default/MessageProperties.cs

@@ -13,13 +13,13 @@ namespace Tapeti.Default
 
 
         /// <inheritdoc />
-        public string ContentType { get; set; }
+        public string? ContentType { get; set; }
 
         /// <inheritdoc />
-        public string CorrelationId { get; set; }
+        public string? CorrelationId { get; set; }
 
         /// <inheritdoc />
-        public string ReplyTo { get; set; }
+        public string? ReplyTo { get; set; }
 
         /// <inheritdoc />
         public bool? Persistent { get; set; }
@@ -37,7 +37,7 @@ namespace Tapeti.Default
 
         /// <summary>
         /// </summary>
-        public MessageProperties(IMessageProperties source)
+        public MessageProperties(IMessageProperties? source)
         {
             if (source == null)
                 return;
@@ -64,7 +64,7 @@ namespace Tapeti.Default
         }
 
         /// <inheritdoc />
-        public string GetHeader(string name)
+        public string? GetHeader(string name)
         {
             return headers.TryGetValue(name, out var value) ? value : null;
         }

Tapeti/Default/PublishResultBinding.cs

@@ -31,7 +31,7 @@ namespace Tapeti.Default
             // Tapeti 1.2: if you just want to publish another message as a result of the incoming message, explicitly call IPublisher.Publish.
             // ReSharper disable once ConvertIfStatementToSwitchStatement
             if (!hasClassResult && expectedClassResult != null || hasClassResult && expectedClassResult != actualType)
-               throw new ArgumentException($"Message handler for non-request message type {context.MessageClass?.FullName} must return type {expectedClassResult?.FullName ?? "void"} in controller {context.Method.DeclaringType?.FullName}, method {context.Method.Name}, found: {actualType?.FullName ?? "void"}");
+               throw new ArgumentException($"Message handler for non-request message type {context.MessageClass?.FullName} must return type {expectedClassResult?.FullName ?? "void"} in controller {context.Method.DeclaringType?.FullName}, method {context.Method.Name}, found: {actualType.FullName ?? "void"}");
 
             if (!hasClassResult)
                 return;
@@ -48,14 +48,22 @@ namespace Tapeti.Default
                     var handler = GetType().GetMethod(nameof(PublishGenericTaskResult), BindingFlags.NonPublic | BindingFlags.Static)?.MakeGenericMethod(actualType);
                     Debug.Assert(handler != null, nameof(handler) + " != null");
 
-                    context.Result.SetHandler((messageContext, value) => (ValueTask)handler.Invoke(null, new[] { messageContext, value }));
+                    context.Result.SetHandler((messageContext, value) =>
+                    {
+                        var result = handler.Invoke(null, new[] { messageContext, value });
+                        return result != null ? (ValueTask)result : ValueTask.CompletedTask;
+                    });
                     break;
 
                 case TaskType.ValueTask:
                     var valueTaskHandler = GetType().GetMethod(nameof(PublishGenericValueTaskResult), BindingFlags.NonPublic | BindingFlags.Static)?.MakeGenericMethod(actualType);
                     Debug.Assert(valueTaskHandler != null, nameof(handler) + " != null");
 
-                    context.Result.SetHandler((messageContext, value) => (ValueTask)valueTaskHandler.Invoke(null, new[] { messageContext, value }));
+                    context.Result.SetHandler((messageContext, value) =>
+                    {
+                        var result = valueTaskHandler.Invoke(null, new[] { messageContext, value });
+                        return result != null ? (ValueTask)result : ValueTask.CompletedTask;
+                    });
                     break;
 
                 default:
@@ -79,7 +87,7 @@ namespace Tapeti.Default
         }
 
 
-        private static async ValueTask Reply(object message, IMessageContext messageContext)
+        private static async ValueTask Reply(object? message, IMessageContext messageContext)
         {
             if (message == null)
                 throw new ArgumentException("Return value of a request message handler must not be null");

Tapeti/Default/RabbitMQMessageProperties.cs

@@ -15,21 +15,21 @@ namespace Tapeti.Default
 
 
         /// <inheritdoc />
-        public string ContentType
+        public string? ContentType
         {
             get => BasicProperties.IsContentTypePresent() ? BasicProperties.ContentType : null;
             set { if (!string.IsNullOrEmpty(value)) BasicProperties.ContentType = value; else BasicProperties.ClearContentType(); }
         }
 
         /// <inheritdoc />
-        public string CorrelationId
+        public string? CorrelationId
         {
             get => BasicProperties.IsCorrelationIdPresent() ? BasicProperties.CorrelationId : null;
             set { if (!string.IsNullOrEmpty(value)) BasicProperties.CorrelationId = value; else BasicProperties.ClearCorrelationId(); }
         }
 
         /// <inheritdoc />
-        public string ReplyTo
+        public string? ReplyTo
         {
             get => BasicProperties.IsReplyToPresent() ? BasicProperties.ReplyTo : null;
             set { if (!string.IsNullOrEmpty(value)) BasicProperties.ReplyTo = value; else BasicProperties.ClearReplyTo(); }
@@ -66,7 +66,7 @@ namespace Tapeti.Default
 
         /// <summary>
         /// </summary>
-        public RabbitMQMessageProperties(IBasicProperties basicProperties, IMessageProperties source)
+        public RabbitMQMessageProperties(IBasicProperties basicProperties, IMessageProperties? source)
         {
             BasicProperties = basicProperties;
             if (source == null)
@@ -97,7 +97,7 @@ namespace Tapeti.Default
 
 
         /// <inheritdoc />
-        public string GetHeader(string name)
+        public string? GetHeader(string name)
         {
             if (BasicProperties.Headers == null)
                 return null;

Tapeti/Default/TypeNameRoutingKeyStrategy.cs

@@ -60,7 +60,7 @@ namespace Tapeti.Default
         }
 
 
-        private static List<string> SplitPascalCase(string value)
+        private static List<string>? SplitPascalCase(string value)
         {
             var split = SeparatorRegex.Split(value);
             if (split.Length == 0)

Tapeti/Helpers/ConnectionstringParser.cs

@@ -10,7 +10,7 @@ namespace Tapeti.Helpers
     /// </summary>
     public class ConnectionStringParser
     {
-        private readonly TapetiConnectionParams result = new TapetiAppSettingsConnectionParams();
+        private readonly TapetiConnectionParams result = new();
 
         private readonly string connectionstring;
         private int pos = -1;

Tapeti/Helpers/DictionaryHelper.cs

@@ -10,7 +10,7 @@ namespace Tapeti.Helpers
         /// <summary>
         /// Checks if two dictionaries are considered compatible. If either is null they are considered empty.
         /// </summary>
-        public static bool NullSafeSameValues(this IReadOnlyDictionary<string, object> arguments1, IReadOnlyDictionary<string, object> arguments2)
+        public static bool NullSafeSameValues(this IReadOnlyDictionary<string, object>? arguments1, IReadOnlyDictionary<string, object>? arguments2)
         {
             if (arguments1 == null || arguments2 == null)
                 return (arguments1 == null || arguments1.Count == 0) && (arguments2 == null || arguments2.Count == 0);

Tapeti/Helpers/ExpressionInvoker.cs

@@ -16,7 +16,7 @@ namespace Tapeti.Helpers
     /// </summary>
     /// <param name="target">The instance on which the method should be called.</param>
     /// <param name="args">The arguments passed to the method.</param>
-    public delegate object ExpressionInvoke(object target, params object[] args);
+    public delegate object ExpressionInvoke(object? target, params object?[] args);
 
 
     /// <summary>

Tapeti/Helpers/MiddlewareHelper.cs

@@ -16,7 +16,7 @@ namespace Tapeti.Helpers
         /// <param name="handle">Receives the middleware which should be called and a reference to the action which will call the next. Pass this on to the middleware.</param>
         /// <param name="lastHandler">The action to execute when the innermost middleware calls next.</param>
         /// <typeparam name="T"></typeparam>
-        public static void Go<T>(IReadOnlyList<T> middleware, Action<T, Action> handle, Action lastHandler)
+        public static void Go<T>(IReadOnlyList<T>? middleware, Action<T, Action> handle, Action lastHandler)
         {
             var handlerIndex = middleware?.Count - 1 ?? -1;
             if (middleware == null || handlerIndex == -1)
@@ -45,7 +45,7 @@ namespace Tapeti.Helpers
         /// <param name="handle">Receives the middleware which should be called and a reference to the action which will call the next. Pass this on to the middleware.</param>
         /// <param name="lastHandler">The action to execute when the innermost middleware calls next.</param>
         /// <typeparam name="T"></typeparam>
-        public static async ValueTask GoAsync<T>(IReadOnlyList<T> middleware, Func<T, Func<ValueTask>, ValueTask> handle, Func<ValueTask> lastHandler)
+        public static async ValueTask GoAsync<T>(IReadOnlyList<T>? middleware, Func<T, Func<ValueTask>, ValueTask> handle, Func<ValueTask> lastHandler)
         {
             var handlerIndex = middleware?.Count - 1 ?? -1;
             if (middleware == null || handlerIndex == -1)

Tapeti/IConnection.cs

@@ -7,19 +7,27 @@ using System.Threading.Tasks;
 namespace Tapeti
 {
     /// <summary>
-    /// 
+    /// Contains information about the established connection.
     /// </summary>
     public class ConnectedEventArgs
     {
         /// <summary>
         /// The connection parameters used to establish the connection.
         /// </summary>
-        public TapetiConnectionParams ConnectionParams;
+        public TapetiConnectionParams ConnectionParams { get; }
 
         /// <summary>
         /// The local port for the connection. Useful for identifying the connection in the management interface.
         /// </summary>
-        public int LocalPort;
+        public int LocalPort { get; }
+
+
+        /// <summary></summary>
+        public ConnectedEventArgs(TapetiConnectionParams connectionParams, int localPort)
+        {
+            ConnectionParams = connectionParams;
+            LocalPort = localPort;
+        }
     }
 
 
@@ -31,12 +39,20 @@ namespace Tapeti
         /// <summary>
         /// The ReplyCode as indicated by the client library
         /// </summary>
-        public ushort ReplyCode;
+        public ushort ReplyCode { get; }
 
         /// <summary>
         /// The ReplyText as indicated by the client library
         /// </summary>
-        public string ReplyText;
+        public string ReplyText { get; }
+
+
+        /// <summary></summary>
+        public DisconnectedEventArgs(ushort replyCode, string replyText)
+        {
+            ReplyCode = replyCode;
+            ReplyText = replyText;
+        }
     }
 
 

Tapeti/ILogger.cs

@@ -32,7 +32,7 @@ namespace Tapeti
         /// <summary>
         /// The exception that caused the connection to fail.
         /// </summary>
-        Exception Exception { get; }
+        Exception? Exception { get; }
     }
 
 
@@ -138,7 +138,7 @@ namespace Tapeti
         /// <param name="queueName">The name of the queue that is declared</param>
         /// <param name="existingArguments">The x-arguments of the existing queue</param>
         /// <param name="arguments">The x-arguments of the queue that would be declared</param>
-        void QueueExistsWarning(string queueName, IRabbitMQArguments existingArguments, IRabbitMQArguments arguments);
+        void QueueExistsWarning(string queueName, IRabbitMQArguments? existingArguments, IRabbitMQArguments? arguments);
 
         /// <summary>
         /// Called before a binding is added to a queue.

Tapeti/IMessageSerializer.cs

@@ -21,6 +21,6 @@ namespace Tapeti
         /// <param name="body">The encoded message</param>
         /// <param name="properties">The properties as sent along with the message</param>
         /// <returns>A decoded instance of the message</returns>
-        object Deserialize(byte[] body, IMessageProperties properties);
+        object? Deserialize(byte[] body, IMessageProperties properties);
     }
 }

Tapeti/IPublisher.cs

@@ -29,7 +29,7 @@ namespace Tapeti
         /// </remarks>
         /// <param name="responseMethodSelector">An expression defining the method which handles the response. Example: c => c.HandleResponse</param>
         /// <param name="message">The message to send</param>
-        Task PublishRequest<TController, TRequest, TResponse>(TRequest message, Expression<Func<TController, Action<TResponse>>> responseMethodSelector) where TController : class;
+        Task PublishRequest<TController, TRequest, TResponse>(TRequest message, Expression<Func<TController, Action<TResponse>>> responseMethodSelector) where TController : class where TRequest : class where TResponse : class;
 
 
         /// <summary>
@@ -42,7 +42,7 @@ namespace Tapeti
         /// </remarks>
         /// <param name="responseMethodSelector">An expression defining the method which handles the response. Example: c => c.HandleResponse</param>
         /// <param name="message">The message to send</param>
-        Task PublishRequest<TController, TRequest, TResponse>(TRequest message, Expression<Func<TController, Func<TResponse, Task>>> responseMethodSelector) where TController : class;
+        Task PublishRequest<TController, TRequest, TResponse>(TRequest message, Expression<Func<TController, Func<TResponse, Task>>> responseMethodSelector) where TController : class where TRequest : class where TResponse : class;
 
 
         /// <summary>
@@ -69,7 +69,7 @@ namespace Tapeti
         /// <param name="message">An instance of a message class</param>
         /// <param name="properties">Metadata to include in the message</param>
         /// <param name="mandatory">If true, an exception will be raised if the message can not be delivered to at least one queue</param>
-        Task Publish(object message, IMessageProperties properties, bool mandatory);
+        Task Publish(object message, IMessageProperties? properties, bool mandatory);
 
 
         /// <summary>
@@ -80,6 +80,6 @@ namespace Tapeti
         /// <param name="properties">Metadata to include in the message</param>
         /// <param name="mandatory">If true, an exception will be raised if the message can not be delivered to the queue</param>
         /// <returns></returns>
-        Task PublishDirect(object message, string queueName, IMessageProperties properties, bool mandatory);
+        Task PublishDirect(object message, string queueName, IMessageProperties? properties, bool mandatory);
     }
 }

Tapeti/Tapeti.csproj

@@ -12,6 +12,7 @@
     <PackageProjectUrl>https://github.com/MvRens/Tapeti</PackageProjectUrl>
     <PackageIcon>Tapeti.png</PackageIcon>
     <LangVersion>9</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">

Tapeti/TapetiConfig.cs

@@ -17,7 +17,7 @@ namespace Tapeti
     /// </summary>
     public class TapetiConfig : ITapetiConfigBuilderAccess
     {
-        private Config config;
+        private Config? config;
         private readonly List<IControllerBindingMiddleware> bindingMiddleware = new();
 
 
@@ -92,10 +92,7 @@ namespace Tapeti
 
             var configInstance = GetConfig();
 
-            var middlewareBundle = extension.GetMiddleware(DependencyResolver);
+            foreach (var middleware in extension.GetMiddleware(DependencyResolver))
-            if (middlewareBundle != null)
-            {
-                foreach (var middleware in middlewareBundle)
             {
                 switch (middleware)
                 {
@@ -113,8 +110,7 @@ namespace Tapeti
 
                     default:
                         throw new ArgumentException(
-                                $"Unsupported middleware implementation: {middleware?.GetType().Name ?? "null"}");
+                            $"Unsupported middleware implementation: {middleware.GetType().Name}");
-                    }
                 }
             }
 
@@ -123,7 +119,7 @@ namespace Tapeti
                 return this;
 
             foreach (var binding in bindingBundle)
-                config.RegisterBinding(binding);
+                GetConfig().RegisterBinding(binding);
 
             return this;
         }
@@ -313,17 +309,23 @@ namespace Tapeti
 
         internal class ConfigBindings : List<IBinding>, ITapetiConfigBindings
         {
-            private Dictionary<MethodInfo, IControllerMethodBinding> methodLookup;
+            private Dictionary<MethodInfo, IControllerMethodBinding>? methodLookup;
 
 
-            public IControllerMethodBinding ForMethod(Delegate method)
+            public IControllerMethodBinding? ForMethod(Delegate method)
             {
+                if (methodLookup == null)
+                    throw new InvalidOperationException("Lock must be called first");
+
                 return methodLookup.TryGetValue(method.Method, out var binding) ? binding : null;
             }
 
 
-            public IControllerMethodBinding ForMethod(MethodInfo method)
+            public IControllerMethodBinding? ForMethod(MethodInfo method)
             {
+                if (methodLookup == null)
+                    throw new InvalidOperationException("Lock must be called first");
+
                 return methodLookup.TryGetValue(method, out var binding) ? binding : null;
             }
 

Tapeti/TapetiConfigControllers.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Linq;
 using System.Reflection;
+using System.Text;
 using Tapeti.Annotations;
 using Tapeti.Config;
 using Tapeti.Connection;
@@ -49,12 +50,7 @@ namespace Tapeti
             {
                 var methodIsObsolete = controllerIsObsolete || method.GetCustomAttribute<ObsoleteAttribute>() != null;
 
-                var context = new ControllerBindingContext(method.GetParameters(), method.ReturnParameter)
+                var context = new ControllerBindingContext(controller, method, method.GetParameters(), method.ReturnParameter);
-                {
-                    Controller = controller,
-                    Method = method
-                };
-
 
                 if (method.GetCustomAttribute<ResponseHandlerAttribute>() != null)
                     context.SetBindingTargetMode(BindingTargetMode.Direct);
@@ -124,11 +120,15 @@ namespace Tapeti
         /// <param name="builder"></param>
         public static ITapetiConfigBuilder RegisterAllControllers(this ITapetiConfigBuilder builder)
         {
-            return RegisterAllControllers(builder, Assembly.GetEntryAssembly());
+            var assembly = Assembly.GetEntryAssembly();
+            if (assembly == null)
+                throw new InvalidOperationException("No EntryAssembly");
+
+            return RegisterAllControllers(builder, assembly);
         }
 
 
-        private static ControllerMethodBinding.QueueInfo GetQueueInfo(MemberInfo member, ControllerMethodBinding.QueueInfo fallbackQueueInfo)
+        private static ControllerMethodBinding.QueueInfo? GetQueueInfo(MemberInfo member, ControllerMethodBinding.QueueInfo? fallbackQueueInfo)
         {
             var dynamicQueueAttribute = member.GetCustomAttribute<DynamicQueueAttribute>();
             var durableQueueAttribute = member.GetCustomAttribute<DurableQueueAttribute>();
@@ -157,26 +157,33 @@ namespace Tapeti
             }
             else
             {
-                queueType = fallbackQueueInfo.QueueType;
+                queueType = fallbackQueueInfo!.QueueType;
                 name = fallbackQueueInfo.Name;
             }
 
-            return new ControllerMethodBinding.QueueInfo
+            return new ControllerMethodBinding.QueueInfo(queueType, name)
             {
-                QueueType = queueType,
-                Name = name,
                 QueueArguments = GetQueueArguments(queueArgumentsAttribute) ?? fallbackQueueInfo?.QueueArguments
             };
         }
 
 
-        private static IRabbitMQArguments GetQueueArguments(QueueArgumentsAttribute queueArgumentsAttribute)
+        private static IRabbitMQArguments? GetQueueArguments(QueueArgumentsAttribute? queueArgumentsAttribute)
         {
             if (queueArgumentsAttribute == null)
                 return null;
 
-            var arguments = new RabbitMQArguments(queueArgumentsAttribute.CustomArguments);
+            var arguments = new RabbitMQArguments(queueArgumentsAttribute.CustomArguments.ToDictionary(
+                    p => p.Key, 
+                    p => p.Value switch
+                    {
+                        string stringValue => Encoding.UTF8.GetBytes(stringValue),
+                        _ => p.Value
+                    }
+                ))
+            {
 
+            };
             if (queueArgumentsAttribute.MaxLength > 0)
                 arguments.Add(@"x-max-length", queueArgumentsAttribute.MaxLength);
 

Tapeti/TapetiConnection.cs

@@ -24,10 +24,10 @@ namespace Tapeti
         /// This property must be set before first subscribing or publishing, otherwise it
         /// will use the default connection parameters.
         /// </remarks>
-        public TapetiConnectionParams Params { get; set; }
+        public TapetiConnectionParams? Params { get; set; }
 
         private readonly Lazy<ITapetiClient> client;
-        private TapetiSubscriber subscriber;
+        private TapetiSubscriber? subscriber;
 
         private bool disposed;
 
@@ -48,13 +48,13 @@ namespace Tapeti
         }
 
         /// <inheritdoc />
-        public event ConnectedEventHandler Connected;
+        public event ConnectedEventHandler? Connected;
 
         /// <inheritdoc />
-        public event DisconnectedEventHandler Disconnected;
+        public event DisconnectedEventHandler? Disconnected;
 
         /// <inheritdoc />
-        public event ConnectedEventHandler Reconnected;
+        public event ConnectedEventHandler? Reconnected;
 
 
         /// <inheritdoc />

Tapeti/TapetiConnectionParams.cs

@@ -10,7 +10,7 @@ namespace Tapeti
     /// </summary>
     public class TapetiConnectionParams
     {
-        private IDictionary<string, string> clientProperties;
+        private IDictionary<string, string>? clientProperties;
 
 
         /// <summary>
@@ -59,7 +59,7 @@ namespace Tapeti
         /// If any of the default keys used by the RabbitMQ Client library (product, version) are specified their value
         /// will be overwritten. See DefaultClientProperties in Connection.cs in the RabbitMQ .NET client source for the default values.
         /// </remarks>
-        public IDictionary<string, string> ClientProperties { 
+        public IDictionary<string, string>? ClientProperties { 
             get => clientProperties ??= new Dictionary<string, string>();
             set => clientProperties = value;
         }

Tapeti/Tasks/SingleThreadTaskQueue.cs

@@ -120,7 +120,7 @@ namespace Tapeti.Tasks
             {
                 while (true)
                 {
-                    Task task;
+                    Task? task;
                     lock (scheduledTasks)
                     {
                         task = WaitAndDequeueTask();
@@ -133,7 +133,7 @@ namespace Tapeti.Tasks
                 }
             }
 
-            private Task WaitAndDequeueTask()
+            private Task? WaitAndDequeueTask()
             {
                 while (!scheduledTasks.Any() && !disposed)
                     Monitor.Wait(scheduledTasks);