FOS\UserBundle\Util\Canonicalizer::canonicalize PHP Method

    public function canonicalize($string)
    {
        return mb_convert_case($string, MB_CASE_LOWER, mb_detect_encoding($string));
    }

 public function canonicalize($string)
 {
     if (extension_loaded('mbstring')) {
         return parent::canonicalize($string);
     } else {
         return strtolower($string);
     }
 }