So if you move the compiler out of the C standard respecting equation then this is a compiler bug? Makes absolutely no sense. This is a C compiler, not a "I would prefer it do that" compiler. You should better define your own langage where dereferencing a NULL pointer is NOT undefined.
The platform is defined by the compiler and the runtime. The compiler definitely has the right to consider that dereferencing a NULL pointer is something that is always undefined, because, well, the standard precisely says that. There is no story of mapping or not mapping pages at this point : NULL pointer dereferencing an undefined behavior is, and NULL pointer dereferencing an undefined behavior stays. A NULL pointer has been dereferenced, the behavior is undefined (and it's not very surprising that an undefined behavior as per a standard can be an exploitable security hole). This is as simple as that.
The bug also is in allowing to map address 0, which can't be a sane way to serve a sane purpose.