I am getting a NullPointerException in my game and I don't know why?

So, I am getting a NullPointerException in the drawToScreen method when I try to draw the image... Does anyone know why?

Java Code:

package com.patrickfeltes.game;

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.image.BufferedImage;

import javax.swing.JPanel;

public class GamePanel extends JPanel implements Runnable {

        public static final int WIDTH = 400;
        public static final int HEIGHT = 300;
        public static final int SCALE = 2;
        
        public static boolean isRunning = false;
        
        private Thread thread;
        
        private static final int targetFPS = 60;
        private long targetTime = 1000 / targetFPS;
        
        private BufferedImage image;
        
        private Graphics g, g2;
        
        public GamePanel() {
                setPreferredSize(new Dimension(WIDTH * SCALE, HEIGHT * SCALE));
                
                start();
        }
        
        public void start() {
                isRunning = true;
                thread = new Thread(this);
                thread.start();
        }


        public void run() {
                
                image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
                
                long start;
                long elapsed;
                long wait;
                
                while(isRunning) {
                        start = System.nanoTime();
                        
                        tick();
                        draw();
                        drawToScreen();
                        
                        elapsed = System.nanoTime() - start;
                        wait = targetTime - elapsed;
                        
                        if(wait < 0) {
                                wait = 17;
                        }
                        
                        try {
                                Thread.sleep(wait);
                        } catch (InterruptedException e) {
                                e.printStackTrace();
                        }
                }
        }
        
        public void tick() {
                
        }
        
        public void draw() {
                g = image.getGraphics();
                g.fillRect(10, 10, 10, 10);
                
        }
        
        public void drawToScreen() {
                g2 = getGraphics();
                g2.drawImage(image, 0, 0, WIDTH * SCALE, HEIGHT * SCALE, null);
        }
        
        
        
}