isset vs empty vs is_null

Question

I\'m trying to write a script that when a user uploads a file and does not enter a name an error is returned. I\'ve tried using is_null, empty, and isset and they all do not

Answer 1

is_null is the dual of isset except isset does not print notices if the variable is null.

>$ciao;
>var_export(is_null($ciao));
>PHP Notice:  Undefined variable: ciao in php shell code on line 1
>true
>var_export(!isset($ciao));
>true