> Now, I know there's a difference between "" and undef in Perl, just like I know there's a difference between "" and NULL in my database.

You do?

Not if your database follows the SQL-92 standard!

Leaving aside the issue of what the SQL-92 standard actually says, and also leaving aside the holy war about whether MySQL is a real database or not, the fact remains that my database, which is MySQL, does treat "" and NULL as different, so my above statement is correct.

In the meantime, I've decided to use a different input validator, which is working much better for me.