Do not use InputBagTypeSpecifyingExtension on true context.

[VincentLanglet]

The InputBag::has method rely on array_key_exists

see
https://github.com/symfony/symfony/blob/e7589c18012314ef262f040357b832a264b2a6eb/src/Symfony/Component/HttpFoundation/ParameterBag.php#L86-L89

So the following code is valid

$inputBag->set('foo', null);
$inputBag->has('foo'); // true
$inputBag->get('foo'); // null

:/

[ondrejmirtes]

Thank you.