Bug report

When overriding DOMDocument::saveHTML(), I get rather random signature mismatches that have nothing to do with the documented signature.

Parameter #1 $node (DOMNode|null) of method ExtendedDocument::saveHTML() is not contravariant with parameter #1 $node (mixed) of method DOMDocument::saveHTML().

Even worse - just returning parent::saveHTML() from the extending method, PHPStan claims the return type does not match, even though it deduced it itself from the parent.

Method ExtendedDocument::saveHTML() should return string but returns string|false.

Code snippet that reproduces the problem

This code snippet replicates the problem: https://phpstan.org/r/f2176152-5861-4451-a9b4-da32795c2b8f

Expected output

The above snippet should not throw any errors.