The definitions of memcpy(), memmove(), and memset() state that
the behaviour is undefined if any of the pointer arguments are
NULL, and some compilers are known to make use of this to
optimise away existing NULL checks in the source.
Change-Id: I489bc256e3eac7ff41d91becb0b43aba73dbb3f9
Link: https://www.imperialviolet.org/2016/06/26/nonnull.html