code: @Override
      public int compare(GregorianCalendar c1, GregorianCalendar c2) {
          if (c2.getGregorianChange() == null) {
              return (int) (c1.getTime().getTime() - c2.getTime().getTime());
          } else {
              return 0;
          }
      }
docs: this method is really suspect, but will ignore this case