NullPointerException

I get Exception in thread "main" java.lang.NullPointerException
at project2.SuperTicTacToePanel.<init>(SuperTicTacToePanel.java:41)
at project2.SuperTicTacToe.main(SuperTicTacToe.java:27)

public class SuperTicTacToe {
	
	/**
	 * 
	 */


	public static void main (String[] args){
		
		JFrame frame = new JFrame ("SuperTicTacToe");
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		
	frame.add (new SuperTicTacToePanel());
		frame.pack();
		frame.setVisible(true);
	}

}
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class SuperTicTacToePanel extends JPanel {
	
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;
	private JButton[][] board;
	private Cell[][] cells;
	private JButton quitButton;
	private ImageIcon xIcon;
	private ImageIcon oIcon;
	private ImageIcon emptyIcon;
	private SuperTicTacToeGame game;
	
	
	
	
	
	

	public SuperTicTacToePanel() {
		
		
		game = new SuperTicTacToeGame();
       
		ButtonListener listener = new ButtonListener();
		
		quitButton.addActionListener(listener);

		quitButton = new JButton("Quit");
		JPanel buttonPanel = new JPanel();
		buttonPanel.setPreferredSize(new Dimension(400, 400));
		buttonPanel.setBackground(Color.MAGENTA);
		JPanel K = new JPanel();
		K.setPreferredSize(new Dimension(50, 400));
		K.setBackground(Color.MAGENTA);
		K.add(quitButton);
		xIcon = new ImageIcon("x.jpg");
		oIcon = new ImageIcon("o.jpg");
		emptyIcon = new ImageIcon("empty.jpg");
		buttonPanel.setLayout(new GridLayout(3, 3));
		add(buttonPanel);
		add(K);
		

		for (int row = 0; row < 3; row++) {

			for (int col = 0; col < 3; col++) {
				this.board[row][col] = new JButton("", emptyIcon);
				board[row][col].addActionListener(listener);
				buttonPanel.add(board[row][col]);
			}
		}
		for (int row = 0; row < 3; row++) {

			for (int col = 0; col < 3; col++) {
				this.board[row][col] = new JButton("", xIcon);
				board[row][col].addActionListener(listener);
				buttonPanel.add(board[row][col]);
			}
		}

		for (int row = 0; row < 3; row++){

			for (int col = 0; col < 3; col++) {
				this.board[row][col] = new JButton("", oIcon);
				board[row][col].addActionListener(listener);
				buttonPanel.add(board[row][col]);
			}}
		}

		private void displayBoard() {
			
			cells = game.getBoard();
			for (int row = 0; row < 3; row++) {
			for (int col = 0; col < 3; col++) {
			if (cells[row][col] == Cell.X) {
			board[row][col].setIcon(xIcon);
			}
			if (cells[row][col] == Cell.O) {
				board[row][col].setIcon(oIcon);
				}
			if (cells[row][col] == Cell.EMPTY) {
				board[row][col].setIcon(emptyIcon);
				}
			}
			}
		}
		
			
			private class ButtonListener implements ActionListener
			{
				
				public void actionPerformed (ActionEvent event){
					for (int row = 0; row < 3; row++) {
						for (int col = 0; col < 3; col++) {
						if (board[row][col] == event.getSource()) {
						// tell the game which button was selected.
						game.select(row,col);
						}
						}
						}
					
					if( quitButton == null)
					{
						System.out.println("stop");
					}
					if (event.getSource() == quitButton)
					{
					System.exit(0);
					}
					 
					 
					displayBoard();
					if (game.getGameStatus() == GameStatus.O_WON) {
						JOptionPane.showMessageDialog(null, "O won and X” + “lost!\n The game will reset");
						}
					if (game.getGameStatus() == GameStatus.X_WON) {
						JOptionPane.showMessageDialog(null, "X won and O” + “lost!\n The game will reset");
						}
					
					
					
				}
				

				
	
	
	
	
	
	
	}
}