code: function _addGraphVertices(db, graph, callback) {
  
    // Get all Stops
    StopsTable.getStops(db, function(err, stops) {
  
      // Database Query Error
      if ( err ) {
        return callback(err);
      }
  
      // Add each Stop as a Vertex
      for ( let i = 0; i < stops.length; i++ ) {
        graph.addNewVertex(stops[i].id, stops[i]);
      }
  
      // Return the Graph
      return callback(null, graph);
  
    });
  
  }
docs: Add all Stops as Vertices to the Graph
  @param {RightTrackDB} db The Right Track DB to query
  @param {Graph} graph The Graph to add vertices to
  @param {function} callback Callback function(err, graph)
  @private