The SFINAE (char(*)[N])(nullptr) trick out of -pedantic

[irrequietus]

Something like (char(*)[N])(nullptr) cannot exist under specific conditions that are of implicit conversion to positive integers / zero when used with such an array type; this is a technique that I often use for sfinae but non-compliant compilers might want to enable zero sized arrays (a GNU extension) by default. Thus, _compilers not respecting this, are not compliant to the standard_ and one of the reasons why -pedantic is on by default on clause. Making a note of this for future reference.