[An extra null pointer check is not needed](https://stackoverflow.com/questions/18775608/free-a-null-pointer-anyway-or-check-first "Free a null pointer anyway or check first?") in macros like “[`SAFE_FREE`](https://github.com/ithewei/libhv/blob/c174588c4c43f8593c5c52c63f85eca9146345c7/base/hdef.h#L216 "Update candidate")”.
