@Override
    public boolean isEqual(@Nullable CommitId val1, @Nullable CommitId val2) {
      if (val1 == val2) return true;
      if (val1 == null || val2 == null) return false;
      return val1.getHash().equals(val2.getHash()) &&
             myRootsReversed.getInt(val1.getRoot()) == myRootsReversed.getInt(val2.getRoot());
    }
@Override
    public boolean isEqual(@Nullable CommitId val1, @Nullable CommitId val2)