I think you are talking about a separate (and identical issue). "NULL" is not a valid memory location. 0 is a valid memory location. Because we have to express

I think you are talking about a separate (and identical issue). "NULL" is not a valid memory location. 0 is a valid memory location. Because we have to express NULL as the same primitive type as valid memory locations, we have no way to distinguish between NULL and 0. In a language with a type system that prevents you from dereferencing NULL, this problem goes away. Now that the type system can distinguish between NULL and a pointer, we can once again use 0 as a valid pointer.