code: function loadGraphSON(graph, filename, callback) {
          var FileInputStream = Tinkerpop.autoImport('FileInputStream');
          var stream = new FileInputStream(filename);
          return Tinkerpop.GraphSONReader.buildP()
              .then(function (builder) {
              return _newGraphSONMapper()
                  .then(function (mapper) { return builder.mapperP(mapper); });
          })
              .then(function (builder) { return builder.createP(); })
              .then(function (reader) { return reader.readGraphP(stream, graph); })
              .then(function () { return graph; })
              .nodeify(callback);
      }
docs: ### `loadGraphSON(graph: Java.Graph, filename: string)` Loads the graph as GraphSON, and returns promise to the graph (for fluent API).