Double Buffering.....problems

Hi srs.

I'm writing a code for a game like Table Tennis and i have to use double buffering to prevent flickering.
The problem is that i have a background picture and another picture attached to the mouse moviments and the current code that i have, compiles but is not working.
Im getting a nullPointerException.
Have anyone experienced something like this??

Here is the code...and exception too.

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import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class PingPong extends Frame {
    public static void main(String[] args) { 
      new PingPong();
    }
    
    PingPong() { 
      super("PingPong v0.02");
            
      addWindowListener(new WindowAdapter() { 
            public void windowClosing(WindowEvent e) { 
                System.exit(0); 
            }
          }); 
            
      pingPongPanel pp = new pingPongPanel(); 
      add(pp);
      pack();
      show();
    }
    
    class pingPongPanel extends Canvas implements MouseMotionListener { 
      int xPos = 0, yPos = 0; 
      int centerX = 35, centerY= 65;
      String bgImage = "Pix/game_arena.jpg", raqte = "Pix/raquete.png";
      Image raquete, bg, bgbuffer;
      Graphics bgOff;

      
      pingPongPanel() {
          raquete = Toolkit.getDefaultToolkit().getImage(this.getClass().getResource(raqte));
          bg = Toolkit.getDefaultToolkit().getImage(this.getClass().getResource(bgImage));

          bgbuffer = createImage(665, 580);
          bgOff = bgbuffer.getGraphics();
          addMouseMotionListener(this);
          setSize(665,580);
      }
      
      public void paint(Graphics g) {
          super.paint(g);
          bgOff.drawImage(bg, 0, 0, this);
          bgOff.drawImage(raquete, xPos - centerX, yPos - centerY, this);
          g.drawImage(bgbuffer, 0, 0, this);
          //g.drawImage(raquete, xPos - centerX, yPos - centerY, this);
      }

      public void update(Graphics g) {
          paint(g);
      }

      public void mouseMoved(MouseEvent event) {
          xPos = event.getX();
          yPos = event.getY();
          //bgbuffer.drawImage(bg, 0, 0, this);
          //bgbuffer.drawImage(raquete, xPos - centerX, yPos - centerY, this);
          repaint();
      } 
            
      public void mouseDragged(MouseEvent event) {}
    }
}

exception:

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fcn@tornado:~/Java/PingPong/src$ javac PingPong.java
fcn@tornado:~/Java/PingPong/src$ java PingPong
Exception in thread "main" java.lang.NullPointerException
        at PingPong$pingPongPanel.<init>(PingPong.java:38)
        at PingPong.<init>(PingPong.java:19)
        at PingPong.main(PingPong.java:7)
fcn@tornado:~/Java/PingPong/src$

Thanx in advance

Fernando