code: @Override
      public void selectionChanged(IAction action, ISelection selection) {
          bugInstance = null;
          // TODO learn to deal with ALL elements
          IMarker marker = MarkerUtil.getMarkerFromSingleSelection(selection);
          if (marker == null) {
              return;
          }
          bugInstance = MarkerUtil.findBugInstanceForMarker(marker);
      }
docs: /*
  (non-Javadoc)
  
  @see
  org.eclipse.ui.IActionDelegate#selectionChanged(org.eclipse.jface.action
  .IAction, org.eclipse.jface.viewers.ISelection)