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
eventBroker.unsubscribe(toBeRenderedHandler);
		eventBroker.unsubscribe(visibilityHandler);
		eventBroker.unsubscribe(childrenHandler);
		eventBroker.unsubscribe(trimHandler);
	}
	private static void populateModelInterfaces(MContext contextModel,
			IEclipseContext context, Class<?>[] interfaces) {
		for (Class<?> intf : interfaces) {
			Activator.trace(Policy.DEBUG_CONTEXTS,
					"Adding " + intf.getName() + " for " 
							+ contextModel.getClass().getName(), null);
			context.set(intf.getName(), contextModel);
			populateModelInterfaces(contextModel, context, intf.getInterfaces());
		}
	}
	private String getContextName(MUIElement element) {
		StringBuilder builder = new StringBuilder(element.getClass()
				.getSimpleName());
		String elementId = element.getElementId();
		if (elementId != null && elementId.length() != 0) {
			builder.append(" (").append(elementId).append(") ");
		}
		builder.append("Context");
		return builder.toString();
	}
	public Object createGui(MUIElement element, Object parentWidget,
			IEclipseContext parentContext) {
		if (!element.isToBeRendered())
			return null;
		if (!renderedElements.contains(element))