public Builder mapper(final Mapper<ObjectMapper> mapper) {
            this.mapper = mapper;
            return this;
        }
Override all of the builder options with this mapper.  If this value is set to something other than
null then that value will be used to construct the writer.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/io/graphson/GraphSONWriter.java