Since this is only used by qtpaths and qmake, let's not make every
application pay the price of dynamically initializing a QString whenever
QtCore is loaded (which 100% of Qt applications do). Instead,
initializing a null pointer costs zero and is one third the size of
QString. Even the assignment in qmake and qtpaths is faster this way.
Pick-to: 6.3
Change-Id: I6fcda969a9e9427198bffffd16ce8d1eb8dc19da
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
8058127a9d