private class StopScanButtonListener implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent e) {
        try {
            portConnection.writeByte((byte) 0xFF);
            portConnection.writeByte((byte) 0x05);
            portConnection.writeByte((byte) 0xFF);
        } catch (SerialPortException | NullPointerException e1) {
            labelState.setText("Ошибка! Возможно вы не подключились к устройству!");
            labelState.repaint();
        }
    }
}