@Override
        public Map<Class, String> getTypeDefinitions() {
            return new HashMap<Class, String>(){{
                put(TinkerGraph.class, "graph");
            }};
        }
Provides a method to serialize an entire {@link TinkerGraph} into itself for GraphSON. This is useful when
shipping small graphs around through Gremlin Server.
tinkergraph-gremlin/src/main/java/org/apache/tinkerpop/gremlin/tinkergraph/structure/TinkerIoRegistryV4.java