@Override
  public @Nullable CommitId getCommitId(int commitIndex) {
    checkDisposed();
    try {
      CommitId commitId = doGetCommitId(commitIndex);
      if (commitId == null) {
        myErrorHandler.handleError(VcsLogErrorHandler.Source.Storage, new RuntimeException("Unknown commit index: " + commitIndex));
      }
      return commitId;
    }
    catch (IOException e) {
      myErrorHandler.handleError(VcsLogErrorHandler.Source.Storage, e);
    }
    return null;
  }
@Override
  public @Nullable CommitId getCommitId(int commitIndex)