Bug 266204 [UI] NPE when 'activating' an empty stack
The Compatibility harness has an (initially) empty EditorStack. Clicking on it produces an NPE because the active part is null
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/workbench/ui/renderers/swt/StackModelFactory.java
@Override
	public <P extends MPart<?>> void processContents(MPart<P> me) {
		Widget parentWidget = getParentWidget(me);
		if (parentWidget == null)
			return;
		
		
		List<P> parts = me.getChildren();
		if (parts != null) {
			for (MPart<?> childME : parts) {
				if (childME.isVisible())
					childAdded(me, childME);
			}
		}
	}
	private CTabItem findItemForPart(MPart<?> folder, MPart<?> part) {
		CTabFolder ctf = (CTabFolder) folder.getWidget();
		if (ctf == null)
			return null;
		CTabItem[] items = ctf.getItems();
		for (int i = 0; i < items.length; i++) {
			if (items[i].getData(OWNING_ME) == part)
				return items[i];
		}
		return null;
	}
	private void hookChildControllerLogic(final MPart<?> parentElement,
			final MPart<?> childElement, final CTabItem cti) {
		
		IObservableValue textObs = EMFObservables.observeValue(