Bug 262707 [CommonNavigator] CommonViewerSorter gets NPE when misconfigured
tests/org.eclipse.ui.tests.navigator/src/org/eclipse/ui/tests/navigator/NavigatorTestBase.java
_commonNavigator = (CommonNavigator) activePage
				.findView(_navigatorInstanceId);
		_commonNavigator.setFocus();
		viewer = (CommonViewer) _commonNavigator.getAdapter(CommonViewer.class);
		contentService = viewer.getNavigatorContentService();
		_actionService = _commonNavigator.getNavigatorActionService();
		IUndoableOperation updateFilters = new UpdateActiveFiltersOperation(
				viewer, new String[0], true);
		updateFilters.execute(null, null);
	}
	protected void tearDown() throws Exception {
		IProject[] projects = ResourcesPlugin.getWorkspace().getRoot()
				.getProjects();
		for (int i = 0; i < projects.length; i++) {
			projects[i].delete(true, null);
		}
		
		EditorTestHelper.showView(_navigatorInstanceId, false);
	}
	
	 
	
	protected void refreshViewer() {
		TreeItem[] rootItems = viewer.getTree().getItems();
		if (rootItems.length > 0)
			rootItems[0].setText("");
		viewer.refresh();
	}
}