mark IAmazonDynamoDbRequestWithKnownKeys as nullable

Author: nhulston

tracer/src/Datadog.Trace/ClrProfiler/AutoInstrumentation/AWS/DynamoDb/IAmazonDynamoDbRequestWithKnownKeys.cs

@@ -3,6 +3,8 @@
 // This product includes software developed at Datadog (https://www.datadoghq.com/). Copyright 2017 Datadog, Inc.
 // </copyright>
 
+#nullable enable
+
 using System.Collections.Generic;
 using System.IO;
 using Datadog.Trace.DuckTyping;