Natural sort does not work for utf32/utf16/ucs2

create or replace table t (fld varchar(1)) default character set ucs2;

insert into t values ('x'),('a'),('b');

select fld, natural_sort_key(fld) from t order by natural_sort_key(fld);

drop table t;

MariaDB [test]> select fld, natural_sort_key(fld) from t order by natural_sort_key(fld);

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

| fld  | natural_sort_key(fld) |

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

| x    | NULL                  |

| a    | NULL                  |

| b    | NULL                  |

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

3 rows in set (0.002 sec)