@Nullable VcsUser getAuthorForCommit(int commitId) {
    try {
      Collection<Integer> userIds = getKeysForCommit(commitId);
      if (userIds == null || userIds.isEmpty()) {
        return null;
      }
      LOG.assertTrue(userIds.size() == 1);
      return myUserIndexer.getUserById(Objects.requireNonNull(getFirstItem(userIds)));
    }
    catch (IOException e) {
      throw new UncheckedIOException(e);
    }
  }
@Nullable VcsUser getAuthorForCommit(int commitId)