C and C++ could have non_nullable pointers, easily

Well, xmalloc has all those effects, but that's the *point* of xmalloc, so I don't see what it has to do type-distinguishing nullable and non-nullable pointers... the point of which is to force people to think about whether a pointer can be null every time they want to dereference it, in a relatively painless way.

(This is all relatively common in languages with real type systems.)