I've gotten into arguments about this in the past.

As you've shown, references can be null, but theyre not supposed to be and are assumed nearly universally to not be.

The argument comes down to when the undefined behavior occurs: is it at the deference to create the reference, or is it on the first memory access using the reference? The language pedants will say the former, but in practice, it's the latter.

In practice, you'll likely be able to invoke a member function on a null pointer or reference, as long as that member doesn't directly or indirectly access data members, or virtual functions of the type. Obligatory, I dont recommend doing this or relying upon this behavior, it's just behavior I've seen in my 2 decades of debugging C++.