It actually doesn't log empty strings (The console would spam empty lines). The emptyString() function is constexpr and generates an empty string at compile-time, which is then passed to InternalLog() using a stream operator. This is useful to check at compile-time if the logging function signatures are valid, in case the code switched to a different mode (e.g. MODE_LPP). Inside InternalLog(), the following constructor and destructor are invoked:

class InternalLog() {
public:
  InternalLog() {
    should_print_ = false;
  };

 virtual ~InternalLog() {
    if (!should_print_) {
      return; //Returns here
    }
   //print logic here
  }
}

When utilizing the LPP_CAPTURE_STDOUT() macro during unittesting, an empty string is returned if nothing is printed.