NULL
as MySQL 8 in opposite to MariaDB 10 does not support the time `0000-00-00 00:00:00` fixes #51 Signed-off-by: Knut Ahlers <knut@ahlers.me>
which didn't work as `string` is a `LONGTEXT` field which cannot fully be indexed while MariaDB does not have those issues. Signed-off-by: Knut Ahlers <knut@ahlers.me>