Bug 341273 ESS will not work without parts
While windows without any parts probably isn't a very interesting shape, it is still possible to create such a thing. In this scenario, the ESS may not work properly because we rely solely on the active part for selection information. It should be possible to have a selection at the window level as-is.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/ESelectionServiceTest.java
private MPart part;
		private Object selection;
		public void reset() {
			part = null;
			selection = null;
		}
		public void selectionChanged(MPart part, Object selection) {
			this.part = part;
			this.selection = selection;
		}
		public MPart getPart() {
			return part;
		}
		public Object getSelection() {
			return selection;
		}
	}
}