Mysql…

mysql> create table foo (bar int);
Query OK, 0 rows affected (0.00 sec)

mysql> insert into foo values ('');
Query OK, 1 row affected (0.00 sec)

Uh… it is not ok!

Lucky I caught that one, as an administrative interface was setting a value to 0 that should have just been NULL, meaning that instead of using a default value for a minimum threshold, it would have used 0, thus setting up a chain of events with unpleasant consequences.