#vulnerable code 
                              @Override
  public void update(EventSubject es) {
    OverlayCapturePrompt cp = null;
    ScreenImage simg = cp.getSelection();
    Screen.closePrompt();
    if (simg != null) {
      try {
        Thread.sleep(300);
      } catch (InterruptedException ie) {
      }
      Rectangle roi = simg.getROI();
      _x = (int) roi.getX();
      _y = (int) roi.getY();
      _w = (int) roi.getWidth();
      _h = (int) roi.getHeight();
      BufferedImage img = getRegionImage(_x, _y, _w, _h);
      setIcon(new ImageIcon(img));
      setToolTipText(this.toString());
    }
    Screen.resetPrompt(cp);
    SikuliIDE.getInstance().setVisible(true);
  } 
                            #location 4 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                              @Override
  public void update(EventSubject es) {
    OverlayCapturePrompt ocp = (OverlayCapturePrompt) es;
    ScreenImage simg = ocp.getSelection();
    Screen.closePrompt();
    if (simg != null) {
      try {
        Thread.sleep(300);
      } catch (InterruptedException ie) {
      }
      Rectangle roi = simg.getROI();
      _x = (int) roi.getX();
      _y = (int) roi.getY();
      _w = (int) roi.getWidth();
      _h = (int) roi.getHeight();
      BufferedImage img = getRegionImage(_x, _y, _w, _h);
      setIcon(new ImageIcon(img));
      setToolTipText(this.toString());
    }
    Screen.resetPrompt(ocp);
    SikuliIDE.showAgain();
  }