code: function(modelItem) {
  			if(!modelItem){
  				return null;
  			}
  			var modelId = this._model.getId(modelItem);
  			if(this._dict[modelId]){
  				this._dict[modelId].gridChildren = null;
  			}
  		}
docs: Initialize the grid navigation holder to null.
  @param {Object} modelItem The model item object that represent a row.