code: function _toNQuads(dataset) {
    var quads = [];
    for(var graphName in dataset) {
      var triples = dataset[graphName];
      for(var ti = 0; ti < triples.length; ++ti) {
        var triple = triples[ti];
        if(graphName === '@default') {
          graphName = null;
        }
        quads.push(_toNQuad(triple, graphName));
      }
    }
    quads.sort();
    return quads.join('');
  }
docs: Converts an RDF dataset to N-Quads.
  
  @param dataset the RDF dataset to convert.
  
  @return the N-Quads string.