Output parameter is not assigned when rising SIGNAL (Class >= '02' (exception))

MariaDB [test]> SELECT VERSION();

+-------------------+

| VERSION()         |

+-------------------+

| 10.1.12-MariaDB-1 |

+-------------------+

1 row in set (0.00 sec)

MariaDB [test]> DROP PROCEDURE IF EXISTS `sp_bug`;

Query OK, 0 rows affected, 1 warning (0.00 sec)

MariaDB [test]> DELIMITER //

MariaDB [test]> CREATE PROCEDURE `sp_bug`(OUT `out_parameter` INT UNSIGNED)

    -> BEGIN

    ->     DECLARE EXIT HANDLER FOR SQLEXCEPTION

    ->     BEGIN

    ->         SET `out_parameter` := 2;

    ->         SELECT `out_parameter`;        

    ->         RESIGNAL;

    ->     END;

    ->     SET `out_parameter` := 1;

    ->     SELECT `out_parameter`;

    ->     SIGNAL SQLSTATE '45000' SET

    ->         MYSQL_ERRNO = 2,

    ->         MESSAGE_TEXT = 'Too long';

    -> END//

Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> DELIMITER ;

MariaDB [test]> SET @`out_parameter` := NULL;

Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> CALL `sp_bug`(@`out_parameter`);

+-----------------+

| `out_parameter` |

+-----------------+

|               1 |

+-----------------+

1 row in set (0.00 sec)

+-----------------+

| `out_parameter` |

+-----------------+

|               2 |

+-----------------+

1 row in set (0.00 sec)

ERROR 2 (45000): Too long

MariaDB [test]> SHOW WARNINGS;

+-------+------+----------+

| Level | Code | Message  |

+-------+------+----------+

| Error |    2 | Too long |

+-------+------+----------+

1 row in set (0.00 sec)

MariaDB [test]> SELECT @`out_parameter`;

+------------------+

| @`out_parameter` |

+------------------+

| NULL             |

+------------------+

1 row in set (0.00 sec)