Bug 81426 Package Explorer shows nothing after drill into working set, then show projects
I200412160800 - switch Package Explorer to working sets - context menu > Go Into a working set - Show > Projects -> view is empty -> view toolbar button 'Up to Working Sets' does not do anything
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/PackageExplorerPart.java
super.init(site, memento);
		fMemento= memento;
		restoreRootMode(fMemento);
		if (showWorkingSets()) {
			createWorkingSetModel();
		}
		restoreLayoutState(memento);
	}
	private void restoreRootMode(IMemento memento) {
		if (memento != null) {
			Integer value= fMemento.getInteger(TAG_ROOT_MODE);
			fRootMode= value == null ? ViewActionGroup.SHOW_PROJECTS : value.intValue();
			if (fRootMode != ViewActionGroup.SHOW_PROJECTS && fRootMode != ViewActionGroup.SHOW_WORKING_SETS)
				fRootMode= ViewActionGroup.SHOW_PROJECTS;
		} else {
			fRootMode= ViewActionGroup.SHOW_PROJECTS;
		}
	}
	private void restoreLayoutState(IMemento memento) {
		Integer state= null;
		if (memento != null)
			state= memento.getInteger(TAG_LAYOUT);
		
		if(state == null) {
			IPreferenceStore store= JavaPlugin.getDefault().getPreferenceStore();
			state= new Integer(store.getInt(TAG_LAYOUT));
		}
		if (state.intValue() == FLAT_LAYOUT)
			fIsCurrentLayoutFlat= true;
		else if (state.intValue() == HIERARCHICAL_LAYOUT)