Bug 262707 [CommonNavigator] CommonViewerSorter gets NPE when misconfigured
tests/org.eclipse.ui.tests.navigator/src/org/eclipse/ui/tests/navigator/NavigatorTestBase.java
public static final String COMMON_NAVIGATOR_RESOURCE_EXT = "org.eclipse.ui.navigator.resourceContent"; 
	public static final String COMMON_NAVIGATOR_JAVA_EXT = "org.eclipse.jdt.java.ui.javaContent"; 
	public static final String COMMON_NAVIGATOR_TEST_EXT = "org.eclipse.ui.tests.navigator.testContent"; 
	public static final String TEST_CONTENT1 = "org.eclipse.ui.tests.navigator.testOverriddenContent1";