@Override
        public void serialize(final Map map, final JsonGenerator jsonGenerator, final SerializerProvider serializerProvider)
                throws IOException {
            for(Map.Entry entry : (Set<Map.Entry>) map.entrySet()) {
                jsonGenerator.writeObject(entry.getKey());
                jsonGenerator.writeObject(entry.getValue());
            }
        }
GraphSON serializers for classes in {@code java.util.*} for the version 3.0 of GraphSON.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/graphson/JavaUtilSerializersV3.java