How to get around the Undefined offset:? error

error_reporting don’t suggest!

What is the point? the apage includes the bpage, before performing certain actions that do not include POST and GET requests, you need to hide the Undefined offset: error.
The error appears as a result of a missing parameter in the array. After performing the action, the error of course disappears!

Answer 1, authority 100%

if(!isset($_POST['some_undefined_key'])){// $_POST    ,   
$_POST['some_undefined_key'] = '';

And… yes. This must be done for all keys (possible in a loop) that the page can request