Bug 49869 NPE showing Type Hierarchies history after layout change
M6 - I retrieve the org.eclipse.swt project from cvs, though this should happen with any java project - select the project in the Package Explorer and press F4 to open a hierarchy view on it - drop down the hierarchy view's Previous Type Hierarchies tool item, it will show 1+ item(s), good - drop down the hierarchy view's dropdown (ie.- the down-pointing triangle in the toolbar) and select Layout -> Horizontal View Orientation - now try to drop down the Previous Type Hierarchies tool item and the attached exception will occur
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/typehierarchy/HistoryDropDownAction.java
public static final int RESULTS_IN_DROP_DOWN= 10;
	private TypeHierarchyViewPart fHierarchyView;
	private Menu fMenu;
	
	public HistoryDropDownAction(TypeHierarchyViewPart view) {
		fHierarchyView= view;
		fMenu= null;
		setToolTipText(TypeHierarchyMessages.getString("HistoryDropDownAction.tooltip")); 
		JavaPluginImages.setLocalImageDescriptors(this, "history_list.gif"); 
		WorkbenchHelp.setHelp(this, IJavaHelpContextIds.TYPEHIERARCHY_HISTORY_ACTION);
		setMenuCreator(this);
	}
	public void dispose() {
		fHierarchyView= null;
		if (fMenu != null) {
			fMenu.dispose();
			fMenu= null;
		}
	}
	public Menu getMenu(Menu parent) {
		return null;
	}
	public Menu getMenu(Control parent) {
		if (fMenu != null) {
			fMenu.dispose();
		}
		fMenu= new Menu(parent);
		IJavaElement[] elements= fHierarchyView.getHistoryEntries();
		boolean checked= addEntries(fMenu, elements);
		if (elements.length > RESULTS_IN_DROP_DOWN) {