IRehydrationContext.TryGetValue - Adding NotNullWhen attribute for out value (#9495)

* Update IGrainLifecycle.cs / IRehydrationContext.TryGetValue - Adding NotNullWhen attribute for out value

* IGrainLifecycle.cs - Fixing missing import for NotNullWhen

* MigrationContext.TryGetValue - Updating to use NotNullWhen attribute for out value

* MigrationContext.TryGetValue - value asserted as not null when returning possibly true

Author: ColinBradley

src/Orleans.Core.Abstractions/Lifecycle/IGrainLifecycle.cs

@@ -2,6 +2,7 @@
 using System;
 using System.Buffers;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Threading;
 
 namespace Orleans.Runtime
@@ -106,6 +107,6 @@ public interface IRehydrationContext
         /// <param name="key">The key.</param>
         /// <param name="value">The value, if present.</param>
         /// <returns><see langword="true"/> if the key exists in the context, otherwise <see langword="false"/>.</returns>
-        bool TryGetValue<T>(string key, out T? value);
+        bool TryGetValue<T>(string key, [NotNullWhen(true)] out T? value);
     }
 }

src/Orleans.Core/Lifecycle/MigrationContext.cs

@@ -3,6 +3,7 @@
 using System.Buffers;
 using System.Collections;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.InteropServices;
 using Orleans.Serialization.Buffers;
 using Orleans.Serialization.Codecs;
@@ -97,7 +98,7 @@ public bool TryGetBytes(string key, out ReadOnlySequence<byte> value)
         return false;
     }
 
-    public bool TryGetValue<T>(string key, out T? value)
+    public bool TryGetValue<T>(string key, [NotNullWhen(true)] out T? value)
     {
         if (_indices.TryGetValue(key, out var record) && _sessionPool.CodecProvider.TryGetCodec<T>() is { } codec)
         {
@@ -106,7 +107,7 @@ public bool TryGetValue<T>(string key, out T? value)
             var reader = Reader.Create(source, session);
             var field = reader.ReadFieldHeader();
             value = codec.ReadValue(ref reader, field);
-            return true;
+            return value is not null;
         }
 
         value = default;