Bug 331685 Unset context from model if widget creation failed since the context is disposed
If the renderer fails to create a widget for a given element, it will dispose its created context (if any) prior to returning from the call. If we try to deconstruct the element later, it will fail with an NPE because the context has been disposed and getParent() will return null.
bundles/org.eclipse.e4.ui.workbench.swt/src/org/eclipse/e4/ui/internal/workbench/swt/PartRenderingEngine.java
if (renderer != null) {
			
			element.setRenderer(renderer);
			Object newWidget = renderer.createWidget(element, parent);
			if (newWidget != null) {
				renderer.bindWidget(element, newWidget);
				return newWidget;
			}
		}
		return null;
	}
	private AbstractPartRenderer getRenderer(MUIElement uiElement, Object parent) {
		return curFactory.getRenderer(uiElement, parent);
	}
	protected AbstractPartRenderer getRendererFor(MUIElement element) {
		return (AbstractPartRenderer) element.getRenderer();
	}
	public Object run(final MApplicationElement uiRoot,
			final IEclipseContext runContext) {
		final Display display;
		if (runContext.get(Display.class) != null) {
			display = runContext.get(Display.class);
		} else {
			display = Display.getDefault();
			runContext.set(Display.class, display);
		}
		Realm.runWithDefault(SWTObservables.getRealm(display), new Runnable() {
			public void run() {
				initializeStyling(display, runContext);