/**
  * Applies filter values provided in URL to a given product collection
  *
  * @param Mage_Catalog_Model_Resource_Eav_Mysql4_Product_Collection $collection
  * @return void
  */
 protected function _applyToCollection($collection)
 {
     if ($this->_isValidCategory($this->getAppliedCategory())) {
         $collection->addCategoryFilter($this->getAppliedCategory());
     }
 }