code: protected function copyFilter($objFilter)
      {
          if ($objFilter) {
              $objNewFilter = $objFilter->createCopy();
          } else {
              $objNewFilter = $this->getEmptyFilter();
          }
          return $objNewFilter;
      }
docs: Clone the given filter or create an empty one if no filter has been passed.
  
  @param IFilter|null $objFilter The filter to clone.
  
  @return IFilter the cloned filter.