public Builder mapper(final Mapper<Kryo> gryoMapper) {
            this.gryoMapper = gryoMapper;
            return this;
        }
Supply a mapper {@link GryoMapper} instance to use as the serializer for the {@code KryoWriter}.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/gryo/GryoReader.java