PHP when md5 returns null value [closed]

I have a question.
So I was doing ctf and there was this if statement. I have no idea how to get past it.
if(isset($_POST['var']) && md5($_POST['var']) == NULL)
All I’m asking for is a little hint, thanks.

Answer

OK, here’s a hint.

PHP’s md5() function expects its argument to be a string.

Can you think of some way of forcing this statement to deal with a different data type?