@Nullable
  public MergeFragment getFragment(int mergeCommit) {
    List<Integer> downNodes = ContainerUtil.sorted(LinearGraphUtils.getDownNodes(myLinearBekGraph, mergeCommit));
    if (downNodes.size() != 2) return null;

    return getFragment(downNodes.get(1), downNodes.get(0), mergeCommit);
  }
@Nullable
  public MergeFragment getFragment(int mergeCommit)