@Override
    public boolean equals(@Nullable VcsUser user1, @Nullable VcsUser user2) {
      if (user1 == user2) return true;
      if (user1 == null || user2 == null) return false;
      return isSamePerson(user1, user2);
    }
@Override
    public boolean equals(@Nullable VcsUser user1, @Nullable VcsUser user2)