NullpointerException error.

			public class GameFrame extends JFrame {

			private JButton[] button = new JButton[9];
                        private JPanel puzpiece;
                        private JFrame frame;
                        
                        public GameFrame() {
                            try {
                                initialize();
                            } catch (IOException e) {
                                e.printStackTrace();
                            }
                        }

			public void initialize() throws IOException {
                            frame = new JFrame();

                        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		        
		         frame.setTitle("Puzzle Game");       
		         frame.setVisible(true);
                // run setImage()
                         setImage();
		        // creates a new panel for the splitted puzzle pieces
		        puzpiece = new JPanel();
		        // set layout of puzpiece panel
		        puzpiece.setLayout(new GridLayout(3,3));
		        // set size of puzpiece panel
		         puzpiece.setPreferredSize(new Dimension(500,200));

		        // adds 9 buttons to puzpiece panel
		             for(int a=0; a<9; a++){
		                 button[a] = new JButton();
		                    puzpiece.add(button[a]);
		             }
		        // add puzpiece panel to JFrame
		        frame.add(puzpiece,BorderLayout.WEST);
                        
                        // set frame size to follow the maximum sizes of all contained components 
                        frame.pack();
                        frame.setLocationRelativeTo(null);
		    }

			    public void setImage() throws IOException{
		        URL img= GameFrame.class.getResource("image/Penguins3.jpg");
		        BufferedImage bi=ImageIO.read(img);
		        int w=bi.getWidth();
		        int h=bi.getHeight();
		        int count=0;
		        for(int i=0;i<3;i++){
		            for(int j=0;j<3;j++){
		                BufferedImage wi=bi.getSubimage(i*w/3,j*h/3, w/3, h/3);
		                Image sc=bi.getScaledInstance(puzpiece.getWidth()/3,


		               puzpiece.getHeight()/3, Image.SCALE_AREA_AVERAGING);
		                setupImage(count++,sc);
		            }
		        }
		    }


		       private void setupImage(int a,Image wi) {
		        button[a]=new JButton(new ImageIcon(wi));
		    }
                       
                       public static void main(String[] args){
                            SwingUtilities.invokeLater(new Runnable() {
                public void run() {
                    GameFrame gf = new GameFrame();
                }
                });
    }
                       }