Add null checks

src/CenterEdge.Async/AsyncHelper.cs

@@ -58,6 +58,16 @@ public static void RunSync(Func<Task> task)
     /// </remarks>
     public static void RunSync<TState>(Func<TState, Task> task, TState state)
     {
+#if NET6_0_OR_GREATER
+        ArgumentNullException.ThrowIfNull(task);
+#else
+        if (task is null)
+        {
+            ThrowHelper.ThrowArgumentNullException(nameof(task));
+            return; // unreachable, but helps static analysis
+        }
+#endif
+
         var oldContext = SynchronizationContext.Current;
 
         if (IsDeadlockSafe(oldContext))
@@ -101,6 +111,16 @@ public static void RunSync<TState>(Func<TState, Task> task, TState state)
     [OverloadResolutionPriority(-1)]
     public static void RunSync(Func<ValueTask> task)
     {
+#if NET6_0_OR_GREATER
+        ArgumentNullException.ThrowIfNull(task);
+#else
+        if (task is null)
+        {
+            ThrowHelper.ThrowArgumentNullException(nameof(task));
+            return; // unreachable, but helps static analysis
+        }
+#endif
+
         RunSync(static state => state.Invoke(), task);
     }
 
@@ -116,6 +136,16 @@ public static void RunSync(Func<ValueTask> task)
     [OverloadResolutionPriority(-1)]
     public static void RunSync<TState>(Func<TState, ValueTask> task, TState state)
     {
+#if NET6_0_OR_GREATER
+        ArgumentNullException.ThrowIfNull(task);
+#else
+        if (task is null)
+        {
+            ThrowHelper.ThrowArgumentNullException(nameof(task));
+            return; // unreachable, but helps static analysis
+        }
+#endif
+
         var oldContext = SynchronizationContext.Current;
 
         if (IsDeadlockSafe(oldContext))
@@ -161,6 +191,16 @@ public static void RunSync<TState>(Func<TState, ValueTask> task, TState state)
     /// </remarks>
     public static T RunSync<T>(Func<Task<T>> task)
     {
+#if NET6_0_OR_GREATER
+        ArgumentNullException.ThrowIfNull(task);
+#else
+        if (task is null)
+        {
+            ThrowHelper.ThrowArgumentNullException(nameof(task));
+            return default!; // unreachable, but helps static analysis
+        }
+#endif
+
         return RunSync(static state => state.Invoke(), task);
     }
 
@@ -176,6 +216,16 @@ public static T RunSync<T>(Func<Task<T>> task)
     /// </remarks>
     public static T RunSync<T, TState>(Func<TState, Task<T>> task, TState state)
     {
+#if NET6_0_OR_GREATER
+        ArgumentNullException.ThrowIfNull(task);
+#else
+        if (task is null)
+        {
+            ThrowHelper.ThrowArgumentNullException(nameof(task));
+            return default!; // unreachable, but helps static analysis
+        }
+#endif
+
         var oldContext = SynchronizationContext.Current;
 
         if (IsDeadlockSafe(oldContext))
@@ -219,6 +269,16 @@ public static T RunSync<T, TState>(Func<TState, Task<T>> task, TState state)
     [OverloadResolutionPriority(-1)]
     public static T RunSync<T>(Func<ValueTask<T>> task)
     {
+#if NET6_0_OR_GREATER
+        ArgumentNullException.ThrowIfNull(task);
+#else
+        if (task is null)
+        {
+            ThrowHelper.ThrowArgumentNullException(nameof(task));
+            return default!; // unreachable, but helps static analysis
+        }
+#endif
+
         return RunSync(static state => state.Invoke(), task);
     }
 
@@ -235,6 +295,16 @@ public static T RunSync<T>(Func<ValueTask<T>> task)
     [OverloadResolutionPriority(-1)]
     public static T RunSync<T, TState>(Func<TState, ValueTask<T>> task, TState state)
     {
+#if NET6_0_OR_GREATER
+        ArgumentNullException.ThrowIfNull(task);
+#else
+        if (task is null)
+        {
+            ThrowHelper.ThrowArgumentNullException(nameof(task));
+            return default!; // unreachable, but helps static analysis
+        }
+#endif
+
         var oldContext = SynchronizationContext.Current;
 
         if (IsDeadlockSafe(oldContext))

src/CenterEdge.Async/CenterEdge.Async.csproj

@@ -29,6 +29,10 @@
     <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.6.3" />
   </ItemGroup>
 
+  <ItemGroup Condition="$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net6.0'))">
+    <Compile Remove="ThrowHelper.cs" />
+  </ItemGroup>
+
   <ItemGroup Condition="$([MSBuild]::IsTargetFrameworkCompatible('$(TargetFramework)', 'net9.0'))">
     <Compile Remove="OverloadResolutionPriorityAttribute.cs" />
   </ItemGroup>

src/CenterEdge.Async/ExclusiveSynchronizationContext.cs

@@ -20,6 +20,16 @@ public override void Send(SendOrPostCallback d, object? state)
 
     public override void Post(SendOrPostCallback d, object? state)
     {
+#if NET6_0_OR_GREATER
+        ArgumentNullException.ThrowIfNull(d);
+#else
+        if (d is null)
+        {
+            ThrowHelper.ThrowArgumentNullException(nameof(d));
+            return; // unreachable, but helps static analysis
+        }
+#endif
+
         try
         {
             _items.Add(new WorkItem(d, state));

src/CenterEdge.Async/ThrowHelper.cs

@@ -0,0 +1,9 @@
+using System;
+
+namespace CenterEdge.Async;
+
+internal class ThrowHelper
+{
+    public static void ThrowArgumentNullException(string paramName) =>
+        throw new ArgumentNullException(paramName);
+}