Always insert null references in the stack when reserving space, instead
of reserving uninitialized space.
This ensures that any attempt to access said values in objects or
strings will result in a null pointer dereference, char = \0, int = 0,
boolean = false. (This is suboptimal for varlocal, since we need N
instructions to reserve N local variables.)
Note that this does not cover object initialization, as that comes from
the simple_malloc routine and the powers-that-be's version just reserves
heap, it does not initialize it.