QSerialPort::isNull() returns always false (even for empty objects)

If a new QSerialPortInfo object is created using the default constructor, isNull() returns false instead of true:

QSerialPortInfo info;
info.isNull(); // returns false (should be true)

The isNull()-method is important for us to check the result of a method that tries to find a serial port by vendor ID and/or product ID:

QSerialPortInfo portInfo = findPortInfo(vendorId, productId);
if (portInfo.isNull()) {
    // port not found
}