attribute ((cleanup(f)): according to the documentation, this variable attribute would call the function f on the variable before exiting the current scope.
I was delighted.

The behavior of malloc(0) is implementation defined by the standard. The two legal possibilities are to return a null pointer or a unique pointer. In many implementations, the second option is accomplished by means of internally increasing the length to 1 (which is then likely rounded up to 16 or so). Legally, one cannot deference this pointer, although in practice some bytes are allocated which means that won’t crash.

Some info on how malloc works

(via links.zirko.me)