FULL PRODUCT VERSION :
java version "1.6.0-rc"
Java(TM) SE Runtime Environment (build 1.6.0-rc-b99)
Java HotSpot(TM) Client VM (build 1.6.0-rc-b99, mixed mode, sharing)
 
But this bug occurs in every version of the JDK from version 1.0.2 onward

ADDITIONAL OS VERSION INFORMATION :
OS independent; occurs in all OS's

A DESCRIPTION OF THE PROBLEM :
Calling java.awt.MenuBar.setHelpMenu(null) is intended to remove the help menu. There is no other way to remove the help menu, and the design of the code clearly shows that this is the intended way to remove the help menu.

However, due to a coding error, it generates a null pointer exception instead. This error was found by FindBugs, and is in fact the only null pointer warning generated by FindBugs on JDK 1.0.2 that still exists in jdk1.6.0-b99.

Here is the relevant code:

 public void setHelpMenu(Menu m) {
        synchronized (getTreeLock()) {
            if (helpMenu == m) {
                return;
            }
            if (helpMenu != null) {
                remove(helpMenu);
            }
            if (m.parent != this) {
                add(m);
            }
            helpMenu = m;
            if (m != null) {
                m.isHelpMenu = true;
                m.parent = this;
                MenuBarPeer peer = (MenuBarPeer)this.peer;
                if (peer != null) {
                    if (m.peer == null) {
                        m.addNotify();
                    }
                    peer.addHelpMenu(m);
                }
            }
        }
    }


The check to see if (m != null) indicates that the developer considered a null
value for m to be a legal value. However, m is dereferenced before then, at
if (m.parent != this), and thus a null pointer exception is generated.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Create a java.awt.MenuBar, set a non-null help menu (using setHelpMenu(...)) and then
set a null help menu (using setHelpMenu(...)).

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The help menu is removed.
ACTUAL -
a null pointer exception occurs

ERROR MESSAGES/STACK TRACES THAT OCCUR :
xception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at java.awt.MenuBar.setHelpMenu(MenuBar.java:164)
	at RemoveHelpMenu$1.actionPerformed(RemoveHelpMenu.java:22)
	at java.awt.MenuItem.processActionEvent(MenuItem.java:597)
	at java.awt.MenuItem.processEvent(MenuItem.java:556)
	at java.awt.MenuComponent.dispatchEventImpl(MenuComponent.java:298)
	at java.awt.MenuComponent.dispatchEvent(MenuComponent.java:286)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:466)
	at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:269)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:190)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:184)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:176)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:110)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.awt.Menu;
import java.awt.MenuBar;
import java.awt.MenuItem;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JFrame;


public class RemoveHelpMenu {
	 MenuBar menuBar;
	    public MenuBar createMenuBar() {
	  
	        //Create the menu bar.
	        menuBar = new MenuBar();
	        
	        Menu helpMenu = new Menu("Help Menu");
	        MenuItem getHelp = new MenuItem("Remove help menu");
	        getHelp.addActionListener(new ActionListener() {

				public void actionPerformed(ActionEvent arg0) {
					menuBar.setHelpMenu(null);
					
				}});
			helpMenu.add(getHelp);
	        
	        menuBar.setHelpMenu(helpMenu);
	        return menuBar;
	    }

	   
	    /**
	     * Create the GUI and show it.  For thread safety,
	     * this method should be invoked from the
	     * event-dispatching thread.
	     */
	    private static void createAndShowGUI() {
	        //Create and set up the window.
	        JFrame frame = new JFrame("RemoveHelpMenu Test");
	        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

	        //Create and set up the content pane.
	        RemoveHelpMenu demo = new RemoveHelpMenu();
	        frame.setMenuBar(demo.createMenuBar());


	        //Display the window.
	        frame.setSize(450, 260);
	        frame.setVisible(true);
	    }

	    public static void main(String[] args) {
	        javax.swing.SwingUtilities.invokeLater(new Runnable() {
	            public void run() {
	                createAndShowGUI();
	            }
	        });
	    }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Don't use help menus, or don't remove them.