Bug 317803 [CommonNavigator] NPE in WorkingSetsContentProvider
bundles/org.eclipse.ui.navigator.resources/src/org/eclipse/ui/internal/navigator/workingsets/WorkingSetsContentProvider.java
extensionStateModel.removePropertyChangeListener(rootModeListener);
	}
	public void inputChanged(Viewer viewer, Object oldInput, Object newInput) {
		if (newInput instanceof IWorkingSet) {
			IWorkingSet rootSet = (IWorkingSet) newInput;
			helper = new WorkingSetHelper(rootSet);
		}
	}
 
	private void updateRootMode() {
		if( extensionStateModel.getBooleanProperty(SHOW_TOP_LEVEL_WORKING_SETS) )
			projectExplorer.setRootMode(ProjectExplorer.WORKING_SETS);
		else
			projectExplorer.setRootMode(ProjectExplorer.PROJECTS);
	}
	protected class WorkingSetHelper {
		private final IWorkingSet workingSet;
		private final Map parents = new WeakHashMap();
		/**
		 * Create a Helper class for the given working set
		 * 
		 * @param set
		 *            The set to use to build the item to parent map.
		 */
		public WorkingSetHelper(IWorkingSet set) {
			workingSet = set;
			if (workingSet.isAggregateWorkingSet()) {
				IAggregateWorkingSet aggregateSet = (IAggregateWorkingSet) workingSet;
				if (workingSetRoot == null)
					workingSetRoot = aggregateSet;