It is invalid to pass null as a pointer argument to memcpy/memcmp/memset, even if the count argument is zero:

> Where an argument declared as size_t n specifies the length of the array for a
function, n can have the value zero on a call to that function. Unless explicitly stated
otherwise in the description of a particular function in this subclause, pointer arguments
on such a call shall still have valid values [...]

Detected by -fsanitize=nonnull-attribute.