Narrowed @param not respected #14968

Bug report

I'm in the process of removing an old parameter, so I changed the type from ?string to null, to get a warning on all places I have not yet replaced it.

simplifed example:

/**
 * @param null $b
 */
function a(?string $b): void
{
	if ($b) echo $b;
}

a(null);
a('test');

Expected a('test'); to complain.

Code snippet that reproduces the problem

https://phpstan.org/r/6776f1bb-56ae-4516-b73c-71b643a36b1f

Expected output

Line 12 Parameter #1 $b of function a expects null, string given.

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