private boolean singleOngoingRebase() {
    Collection<GitRepository> ongoingRebases = getOngoingRebases();
    if (ongoingRebases.size() > 1) {
      LOG.warn("Invalid rebase spec: rebase is in progress in " + getShortNames(ongoingRebases));
      return false;
    }
    return true;
  }
private boolean singleOngoingRebase()