Fix AnyType serialization with empty-string dictionary keys (#9775)

Author: glen-84

src/HotChocolate/Core/src/Types/Text/Json/ResultDocument.cs

@@ -448,6 +448,11 @@ private ReadOnlySpan<byte> ReadRawValue(DbRow row)
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private ReadOnlySpan<byte> ReadLocalData(int location, int size)
     {
+        if (size == 0)
+        {
+            return [];
+        }
+
         var startChunkIndex = location / JsonMemory.BufferSize;
         var offsetInStartChunk = location % JsonMemory.BufferSize;
 
@@ -725,6 +730,11 @@ private void WriteByte(int position, byte value)
 
     private void WriteDataCore(int position, ReadOnlySpan<byte> data)
     {
+        if (data.Length == 0)
+        {
+            return;
+        }
+
         var chunkIndex = position / JsonMemory.BufferSize;
         var offset = position % JsonMemory.BufferSize;
         var availableInChunk = JsonMemory.BufferSize - offset;

src/HotChocolate/Core/src/Types/Text/Json/ResultElement.cs

@@ -931,11 +931,6 @@ public void SetPropertyName(ReadOnlySpan<char> propertyName)
     {
         CheckValidInstance();
 
-        if (propertyName.Length == 0)
-        {
-            throw new ArgumentNullException(nameof(propertyName));
-        }
-
         var encoding = Encoding.UTF8;
         var requiredBytes = encoding.GetByteCount(propertyName);
         byte[]? rented = null;
@@ -961,11 +956,6 @@ public void SetPropertyName(ReadOnlySpan<byte> propertyName)
     {
         CheckValidInstance();
 
-        if (propertyName.Length == 0)
-        {
-            throw new ArgumentNullException(nameof(propertyName));
-        }
-
         _parent.AssignPropertyName(this, propertyName);
     }
 

src/HotChocolate/Core/test/Types.Tests/Types/Scalars/AnyTypeTests.cs

@@ -155,6 +155,39 @@ public async Task Output_Return_RecordList()
         result.ToJson().MatchSnapshot();
     }
 
+    [Fact]
+    public async Task Output_Return_Dictionary_With_Empty_Key()
+    {
+        // arrange
+        var executor =
+            await new ServiceCollection()
+                .AddGraphQLServer()
+                .AddQueryType(
+                    d => d
+                        .Name("Query")
+                        .Field("foo")
+                        .Type<AnyType>()
+                        .Resolve(_ => new Dictionary<string, object?> { [""] = null }))
+                .AddJsonTypeConverter()
+                .BuildRequestExecutorAsync();
+
+        // act
+        var result = (await executor.ExecuteAsync("{ foo }")).ExpectOperationResult();
+
+        // assert
+        Assert.Empty(result.Errors);
+        result.MatchInlineSnapshot(
+            """
+            {
+              "data": {
+                "foo": {
+                  "": null
+                }
+              }
+            }
+            """);
+    }
+
     [Fact]
     public async Task Output_Return_DateTime()
     {