ifnull function does not work on datetime datatype.

The ifnull() function does not work on the datetime data type in mariaDB CS.

Test case:

create table test_nulls_infini
(name varchar(100),
dbdate datetime
)engine=infinidb
;

insert into test_nulls_infini values('test', null)
;

select ifnull(dbdate,now())
from test_nulls_infini
;