code: function(modelItem, lazyCreate) {
  			if(!modelItem){
  				return null;
  			}
  			var modelId = this._model.getId(modelItem);
  			if(this._dict[modelId]){
  				if(!this._dict[modelId].gridChildren && lazyCreate){
  					this._dict[modelId].gridChildren = [];
  				}
  				return this._dict[modelId].gridChildren;
  			}
  			return null;
  		}
docs: Get the grid navigation holder from a row navigation model.
  @param {Object} modelItem The model item object that represent a row.
  @returns {Array} The .gridChildren property of the value keyed by the model id.