private static void writeTypeForGraphObjectIfUntyped(final JsonGenerator jsonGenerator, final TypeInfo typeInfo,
                                                         final String type) throws IOException {
        if (typeInfo == TypeInfo.NO_TYPES) {
            jsonGenerator.writeStringField(GraphSONTokens.TYPE, type);
        }
    }
When doing untyped serialization graph objects get a special "type" field appended.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/graphson/GraphSONSerializersV4.java