I think that the "null issue" is not an issue. Strictly speaking if you
want null or an int - leave out the type hint and use generic argument that
will accept anything.
I think it's over-engineering to try and push a special treatment for the
null. If function/method argument accepts anything but a single type -
it's type-less and does not need a type hint.
Developers should not abuse type hints and adding a special case for
handling null will make many start to request things like this:
function foo(string|array $data)
function foo(bool|int $flag)
function foo(mixed $someVar)
etc.
I'm not sure about you, but I don't wanna see that kind of thing eventually
making it's way into the language (believe me - even I considered that at
some point, but i'm more mature now and more settled in my wishes :))