yii\grid\Column::renderFilterCellContent PHP Method

    protected function renderFilterCellContent()
    {
        return $this->grid->emptyCell;
    }

 protected function renderFilterCellContent()
 {
     $filter = $this->guessFilter();
     if ($filter instanceof BaseFilter) {
         return $filter->render();
     }
     return Column::renderFilterCellContent();
 }