Bug 262707 [CommonNavigator] CommonViewerSorter gets NPE when misconfigured
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/navigator/CommonViewerSorter.java
/**
 * 
 * Provides an implementation of TreeViewerSorter that uses the given parent to determine the
 * correct sort order based on the defined
 * <b>org.eclipse.ui.navigator.navigatorContent/navigatorContent/commonSorter</b> elements
 * available in the set of <i>visible</i> content extensions.
 * 
 * <p>
 * The CommonViewerSorter must be assigned a {@link INavigatorContentService} to drive its sorting
 * algorithm. Without a vaild content service, the sorter will return the default ordering.
 * </p>
 * <p>
 * A CommonViewerSorter may not be attached to more than one CommonViewer.
 * </p>
 * 
 * <p>
 * Clients may not extend this class.
 * </p>
 * 
 * 
 * 
 * @since 3.2
 * 
 */
public final class CommonViewerSorter extends TreePathViewerSorter {
	
	private static final int LEFT_UNDERSTANDS = 1;
	private static final int RIGHT_UNDERSTANDS = 2; 
	private static final int BOTH_UNDERSTAND = LEFT_UNDERSTANDS | RIGHT_UNDERSTANDS; 
	private NavigatorContentService contentService;