@Nullable
  private Map<Repo, VcsFullCommitDetails> convertToSingleElementMap(@NotNull MultiMap<Repo, VcsFullCommitDetails> groupedCommits) {
    Map<Repo, VcsFullCommitDetails> map = new HashMap<>();
    for (Map.Entry<Repo, Collection<VcsFullCommitDetails>> entry : groupedCommits.entrySet()) {
      Collection<VcsFullCommitDetails> commits = entry.getValue();
      if (commits.size() != 1) {
        return null;
      }
      map.put(entry.getKey(), commits.iterator().next());
    }
    return map;
  }
@Nullable
  private Map<Repo, VcsFullCommitDetails> convertToSingleElementMap(@NotNull MultiMap<Repo, VcsFullCommitDetails> groupedCommits)