/**
  * Deletes thumbnail file
  *
  * @param oxArticle $oArticle article object
  *
  * @return null
  */
 protected function _deleteThumbnail($oArticle)
 {
     if ($oArticle->oxarticles__oxthumb->value) {
         if (!$oArticle->isDerived()) {
             $oPicHandler = oxRegistry::get("oxPictureHandler");
             $oPicHandler->deleteThumbnail($oArticle);
         }
         //reseting field
         $oArticle->oxarticles__oxthumb = new oxField();
     }
 }