public Object execute(ExecutionEvent event) throws ExecutionException {
   IHistoryView view =
       TeamUI.showHistoryFor(getPartPage(event), getSelectedResources(event)[0], null);
   if (view == null) return null;
   IHistoryPage page = view.getHistoryPage();
   if (page instanceof GitHistoryPage) {
     GitHistoryPage gitHistoryPage = (GitHistoryPage) page;
     gitHistoryPage.setCompareMode(true);
   }
   return null;
 }