Don't use "NULL" in C++[1].
[1] https://cpp4arduino.com/2018/10/26/why-cpp-programmers-dont-...
[1] https://cpp4arduino.com/2018/10/26/why-cpp-programmers-dont-...
GCC used to use a magic builtin in pre C++11 to implement NULL, but IIRC they removed it as non-conforming.
> Are there any drawbacks to using nullptr instead of NULL? No, unless you target old compilers that don’t support C++11, which is very unlikely.
and OP is specifically targeting c++98.