Minor Description
When implementing GraphBinary as part of TINKERPOP-1942, the idea was to make RequestMessageSerializer and ResponseMessageSerializer implement TypeSerializer<T> interface, but was later disregarded as those are top level serializers (Request/Response can't be nested within another type).
As a result, the nullable parameter was removed from RequestMessageSerializer but I've forgot to do it for ResponseMessageSerializer. We should remove it as it's never used, the question is whether we can do this change as part of a patch release, as it involves API changes. Given that GraphBinary is still on its early stages and ResponseMessageSerializer is not designed to be inherited from / all called, I think we should change the method signature asap.