public static function convertToEncoding($mixed)
    {
        if (is_null(self::$_encoding)
            || is_numeric($mixed)
            || is_bool($mixed)
            || is_object($mixed)
            || is_array($mixed)
            || !is_string($mixed)
            || !function_exists('mb_convert_encoding')
        ) {
            return $mixed;  
        }
        return \mb_convert_encoding($mixed, self::$_encoding);
    }