code: protected function renderFilterCellContent()
      {
          if (is_string($this->filter)) {
              return $this->filter;
          }
  
          $model = $this->grid->filterModel;
  
          if ($this->filter !== false && $model instanceof Model && $this->attribute !== null && $model->isAttributeActive($this->attribute)) {
              if ($model->hasErrors($this->attribute)) {
                  Html::addCssClass($this->filterOptions, 'has-error');
                  $error = ' ' . Html::error($model, $this->attribute, $this->grid->filterErrorOptions);
              } else {
                  $error = '';
              }
              if (is_array($this->filter)) {
                  $options = array_merge(['prompt' => ''], $this->filterInputOptions);
                  return Html::activeDropDownList($model, $this->attribute, $this->filter, $options) . $error;
              } elseif ($this->format === 'boolean') {
                  $options = array_merge(['prompt' => ''], $this->filterInputOptions);
                  return Html::activeDropDownList($model, $this->attribute, [
                      1 => $this->grid->formatter->booleanFormat[1],
                      0 => $this->grid->formatter->booleanFormat[0],
                  ], $options) . $error;
              }
  
              return Html::activeTextInput($model, $this->attribute, $this->filterInputOptions) . $error;
          }
  
          return parent::renderFilterCellContent();
      }
docs: {@inheritdoc}