@Override
        public Io.Builder<? extends Io> onMapper(final Consumer<Mapper.Builder> onMapper) {
            this.onMapper = onMapper;
            return this;
        }
Create a new builder using the specified version of GraphSON.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/graphson/GraphSONIo.java