/**
  * save $file to $dirname as $filename
  *
  * @param string
  * @param string
  * @param string|NULL
  * @param bool overwrite older file with given $filename ?
  * @return string used file name (potential dangerous chars replaced)
  */
 public static function save($file, $dirname, $filename = null, $overwriteOldFile = true)
 {
     try {
         $img = self::checkImage($file, $filename);
     } catch (NoFileUploadedException $e) {
         return null;
     }
     return parent::save($img, $dirname, $filename, $overwriteOldFile);
 }