Thread: I can not display Image

Hi, why wont this work!!! >.<
I get this error

Exception in thread "Thread-2" java.lang.NullPointerException
at main.render(main.java:104)
at main.run(main.java:84)
at java.lang.Thread.run(Unknown Source)

import java.awt.BorderLayout;
import java.awt.Canvas;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
 
public class main extends Canvas implements Runnable {
 
		private static final long serialVersionUID = 1L;
 
		public static final int WIDTH = 240;
		public static final int HEIGHT =  WIDTH/12*9;
		public static final int SCALE = 3;
		public static final String NAME = "Half Life 3";
 
		private JFrame frame;
 
		public boolean running = false;
		public int tickCount = 0;
 
		private	Graphics g ;
 
		private ImageIcon img = new ImageIcon("res\background.jpg");
		private Image back = img.getImage();
 
 
		public main(){
			setMinimumSize(new Dimension(WIDTH*SCALE,HEIGHT*SCALE));
			setMaximumSize(new Dimension(WIDTH*SCALE,HEIGHT*SCALE));
			setPreferredSize(new Dimension(WIDTH*SCALE,HEIGHT*SCALE));
 
			frame = new JFrame(NAME);
			ImageIcon icon  = new ImageIcon("res/Half-life.png");
			frame.setIconImage(icon.getImage());
			frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
			frame.setLayout(new BorderLayout());
 
			frame.add(this,BorderLayout.CENTER);
			frame.pack();
 
			frame.setResizable(false);
			frame.setLocationRelativeTo(null);
			frame.setVisible(true);
 
		}
 
		public void run(){
			long lastTime = System.nanoTime();
			double nsPerTick = 1000000000D/60D; //Nano Sec per tick D represents its type double same as doing .0
 
			int ticks = 0;
			int frames = 0;
 
			long lastTimer = System.currentTimeMillis();
			double delta = 0 ; // How many nano seconds have gone by so far. Once we hit one, we will -1 from it.
 
			init();
 
			while(running){
 
				long now = System.nanoTime();
				delta += (now - lastTime) / nsPerTick;
				lastTime = now;
				boolean shouldRender = true;
				while(delta >= 1){
					ticks++;
					tick();
					delta -=1;
					shouldRender = true;
				}
 
				try{
				Thread.sleep(2);
				}catch(Exception e){}
 
				if(shouldRender){
				frames++;
				render();
				}
 
				if(System.currentTimeMillis() - lastTimer >= 1000){
					lastTimer += 1000;
					System.out.println(ticks+" Ticks, "+frames+" Frames");
					frames = 0;
					ticks = 0;
				}
			}
		}
 
 
		public void tick(){
			tickCount++;
		}
 
		public void render(){
 
		  //  g.drawImage(back,0,0,WIDTH/2,HEIGHT/2,null);
		g.drawRect(0, 0, WIDTH, HEIGHT);
 
		}
 
		public void init(){
			int index = 0;
			//loops through reds green and blues;
		}
 
		public synchronized void start() {
			running = true;
			new Thread(this).start();	
 
		}
 
		public synchronized void stop() {
			running = false;
		}
		public static void main(String [] args){
 
			new main().start();
 
		}
 
 
	}