Numeric aggregates should end up with an error for xmltype

MariaDB [test]>   CREATE TABLE t (x XMLTYPE);

Query OK, 0 rows affected (0,062 sec)

MariaDB [test]>   INSERT INTO t VALUES ('<a/>');

Query OK, 1 row affected (0,010 sec)

MariaDB [test]> INSERT INTO t VALUES ('<a/>'),('<b>1</b>'),('<n>4.5</n>'),('<c/>');

Query OK, 4 rows affected (0,014 sec)

Records: 4  Duplicates: 0  Warnings: 0

MariaDB [test]> select x+1 from t;

ERROR 4078 (HY000): Illegal parameter data types xmltype and int for operation '+'

MariaDB [test]> select sum(x) from t;

+--------+

| sum(x) |

+--------+

|      0 |

+--------+

1 row in set, 5 warnings (0,003 sec)

Warning (Code 1292): Truncated incorrect DOUBLE value: '<a/>'

Warning (Code 1292): Truncated incorrect DOUBLE value: '<a/>'

Warning (Code 1292): Truncated incorrect DOUBLE value: '<b>1</b>'

Warning (Code 1292): Truncated incorrect DOUBLE value: '<n>4.5</n>'

Warning (Code 1292): Truncated incorrect DOUBLE value: '<c/>'