code: function saveGraphSON(graph, filename, callback) {
          var FileOutputStream = Tinkerpop.autoImport('FileOutputStream');
          var stream = new FileOutputStream(filename);
          return Tinkerpop.GraphSONWriter.buildP()
              .then(function (builder) {
              return _newGraphSONMapper()
                  .then(function (mapper) { return builder.mapperP(mapper); });
          })
              .then(function (builder) { return builder.createP(); })
              .then(function (writer) { return writer.writeGraphP(stream, graph); })
              .then(function () { return graph; })
              .nodeify(callback);
      }
docs: ### `saveGraphSON(graph: Java.Graph, filename: string)` Saves the graph as GraphSON, and returns promise to the graph.