Bug 317803 [CommonNavigator] NPE in WorkingSetsContentProvider
bundles/org.eclipse.ui.navigator.resources/src/org/eclipse/ui/internal/navigator/workingsets/WorkingSetsContentProvider.java
/**
	 * The extension id for the WorkingSet extension.
	 */
	public static final String EXTENSION_ID = "org.eclipse.ui.navigator.resources.workingSets"; 
	/**
	 * A key used by the Extension State Model to keep track of whether top level Working Sets or
	 * Projects should be shown in the viewer.
	 */
	public static final String SHOW_TOP_LEVEL_WORKING_SETS = EXTENSION_ID + ".showTopLevelWorkingSets"; 
	private static final Object[] NO_CHILDREN = new Object[0];
	private WorkingSetHelper helper;
	private IAggregateWorkingSet workingSetRoot;
	private IExtensionStateModel extensionStateModel;
	private CommonNavigator projectExplorer;
	private CommonViewer viewer;
	
	private IPropertyChangeListener rootModeListener = new IPropertyChangeListener() {
		
		/* (non-Javadoc)
		 * @see org.eclipse.jface.util.IPropertyChangeListener#propertyChange(org.eclipse.jface.util.PropertyChangeEvent)
		 */
		public void propertyChange(PropertyChangeEvent event) {
			if(SHOW_TOP_LEVEL_WORKING_SETS.equals(event.getProperty())) {
				updateRootMode();
			}
		}
	};
	
	/* (non-Javadoc)
	 * @see org.eclipse.ui.navigator.ICommonContentProvider#init(org.eclipse.ui.navigator.ICommonContentExtensionSite)