regression in QtEmbedded: null QStringList join with null seperator to an empty string, should be null.

#include <QtGui>

int main(int argc, char** argv) {
        QApplication app(argc, argv);
        QStringList list;
        QString str = list.join(QString());
        qWarning() << str.isNull();
        app.exec();
}

    devName = args.join(QString());
    if (devName.isNull()) {
        const char *str = getenv("TSLIB_TSDEVICE");
        if (str)
            devName = QString::fromLocal8Bit(str);
    }