address TODO"

src/csharp/Grpc.Core.Tests/ContextualMarshallerTest.cs

@@ -52,8 +52,8 @@ namespace Grpc.Core.Tests
                     }
                     if (str == "SERIALIZE_TO_NULL")
                     {
-                        // TODO: test for not calling complete Complete() (that resulted in null payload before...)
-                        // TODO: test for calling Complete(null byte array)
+                        // for contextual marshaller, serializing to null payload corresponds
+                        // to not calling the Complete() method in the serializer.
                         return;
                     }
                     var bytes = System.Text.Encoding.UTF8.GetBytes(str);