please fix your expectations according how ternary operator works for many years now, your expected behavior would it make completly useless for 99% of all use cases

You are looking for;

    $a = (int) ($_GET['field'] ?? null);

Casts are high-precedence operators.

Not a bug but expected behaviour.

with proper error reporting you would seewhat really happens:
you are doing (int)$_GET['field'] which is afterward 0 and the ?? is a noop

php > $a = (int) $_GET['field'] ?? null; var_dump($a);
Notice: Undefined index: field in php shell code on line 1

> You are looking for
> $a = (int) ($_GET['field'] ?? null);

won't change anyhing, no way that is line ever results in expected result BULL, it will alway be int 0, one time with warnings and one time without beause in that version you cast the result of ($_GET['field'] ?? null) but you still cast

the only difference is if "?? null" is executed at all

@bugreports: You are right. I skimmed this a bit too quickly. I believe what OP wants is just

    $a = isset($_GET['field']) ? (int) $_GET['field'] : null;

or

    $a = (?int) ($_GET['field'] ?? null);

with a hypothetical nullable cast operator (https://wiki.php.net/rfc/nullable-casting).