Most modern hosts reliably fail when you attempt to dereference a null pointer.
On almost all modern hosts, null pointers use an all-bits-zero internal
representation, so you can reliably use memset with 0 to set all
the pointers in an array to null values.
If p is a null pointer to an object type, the C expression
p + 0 always evaluates to p on modern hosts, even though
the standard says that it has undefined behavior.