Bug 30341 NPE attempting "Show in package explorer" [packge explorer]
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/PackageExplorerPart.java
if (fContextMenu != null && !fContextMenu.isDisposed())
			fContextMenu.dispose();
		getSite().getPage().removePartListener(fPartListener);
		JavaPlugin.getDefault().getPreferenceStore().removePropertyChangeListener(this);
		if (fViewer != null)
			fViewer.removeTreeListener(fExpansionListener);
		
		if (fActionSet != null)	
			fActionSet.dispose();
		super.dispose();	
	}
	/**
	 * Implementation of IWorkbenchPart.createPartControl(Composite)
	 */
	public void createPartControl(Composite parent) {
		
		fViewer= createViewer(parent);
		fViewer.setUseHashlookup(true);
		
		setProviders();
		
		JavaPlugin.getDefault().getPreferenceStore().addPropertyChangeListener(this);
	
		
		MenuManager menuMgr= new MenuManager("#PopupMenu"); 
		menuMgr.setRemoveAllWhenShown(true);
		menuMgr.addMenuListener(this);
		fContextMenu= menuMgr.createContextMenu(fViewer.getTree());
		fViewer.getTree().setMenu(fContextMenu);