Bug 78317 Compare plug-in gets loaded by LocalHistoryActionGroup
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/compare/JavaAddElementFromHistory.java
String errorTitle= CompareMessages.getString("AddFromHistory.title"); 
		String errorMessage= CompareMessages.getString("AddFromHistory.internalErrorMessage"); 
		Shell shell= getShell();
		
		ICompilationUnit cu= null;
		IParent parent= null;
		IMember input= null;
		
		
		if (selection.isEmpty()) {
			
			JavaEditor editor= getEditor();
			if (editor != null) {
				IEditorInput editorInput= editor.getEditorInput();
				IWorkingCopyManager manager= JavaPlugin.getDefault().getWorkingCopyManager();
				if (manager != null) {
					cu= manager.getWorkingCopy(editorInput);
					parent= cu;
				}
			}
		} else {
			input= getEditionElement(selection);
			if (input != null) {
				cu= input.getCompilationUnit();
			
				if (input != null) {
					parent= input;
					input= null;
				}