We want to preserve nullness where possible. Test that various ctors
do the right thing when presented with null input.
Pick-to: 6.3
Change-Id: Ia1a1d4fb3c919b4fed2d9b87827815a1b5072c54
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>