What am I doing wrong?

[YoungBuck]

I'm trying to learn Java and am having problems with a simple applet I am authoring, the purpose of this simple applet is to flip through images passed to the applet as parameters every few seconds. Everything compiles fine but when I try to run it through the appletviewer I get a NullPointerException on the boldface line below...

import java.awt.*;
import java.applet.*;
import java.util.*;

public class ImageFlip extends Applet
{
	
	private Image imgs[];
	private int numimgs = 0;
	private int curimg = 0;
	
	public void init()
	{
	  String name;
	  	
		for(numimgs = 0; (name = getParameter("img" + numimgs)) != null; ++numimgs);
		{
			imgs[numimgs] = getImage(getDocumentBase(), name);
		}
		
	}
	
	public void start()
	{
		
		while(this.isActive() == true);
		{
			paint(getGraphics());
			wait(1000);
		}
	
	}		
	
	private void wait(int millisecs)
	{
	  Date dt = new Date();
	  long strt;
	  
	  strt = dt.getTime();
	  
		while(dt.getTime() - strt < millisecs) {}
		
	
	}
	
	
	public void paint(Graphics g)
	{
		g.drawImage(imgs[++curimg], 0, 0, 500, 400, this);
		if((curimg + 1) >= numimgs) {curimg = 0;}
	}

}