Bug 303305 EPS cannot handle being asked for from the application's context
Right now we have this... @Inject @Named(EPartService.PART_SERVICE_ROOT) private MElementContainer<MUIElement> rootContainer; ...which will be 'null' if the question was posed to the application's context. Right now, I cannot use EPS in the SaveHandler because I get an (effectively) useless EPartService (filled with null fields).
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/workbench/ui/internal/PartServiceImpl.java
MPartDescriptor descriptor = findDescriptor(providedPart.getId());
		if (descriptor == null) {
			if (providedPart != localPart) {
				MPartStack stack = MApplicationFactory.eINSTANCE.createPartStack();
				stack.getChildren().add(providedPart);
				rootContainer.getChildren().add(stack);
			}
		} else {
			if (providedPart != localPart && !descriptor.isAllowMultiple()) {
				return localPart;
			}
			String category = descriptor.getCategory();
			MApplicationElement container = modelService.find(category, rootContainer);
			if (container instanceof MElementContainer<?>) {
				((MElementContainer<MPart>) container).getChildren().add(providedPart);
			} else {
				MPartStack stack = MApplicationFactory.eINSTANCE.createPartStack();
				stack.setId(category);
				stack.getChildren().add(providedPart);
				rootContainer.getChildren().add(stack);
			}
		}
		return providedPart;
	}
	private MPart showExistingPart(PartState partState, MPart providedPart, MPart localPart) {
		MPart part = addPart(providedPart, localPart);
		switch (partState) {
		case ACTIVATE:
			activate(part);
			return part;