No warning after CAST( AS xmltype)

MariaDB [test]> SELECT CAST('a' AS int);

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

| CAST('a' AS int) |

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

|                0 |

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

1 row in set, 1 warning (0,001 sec)

Warning (Code 1292): Truncated incorrect INTEGER value: 'a'

MariaDB [test]> SELECT CAST('a' AS xmltype);

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

| CAST('a' AS xmltype) |

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

| NULL                 |

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

1 row in set (0,009 sec)