code: private static Optional<AbbreviatedObjectId> createAbbreviatedCommitId(@Nonnull ObjectReader objectReader, ObjectId commitId, int requestedLength) {
      if (requestedLength < 2) {
        // 0 means we don't want to print commit id's at all
        return Optional.empty();
      }
  
      try {
        AbbreviatedObjectId abbreviatedObjectId = objectReader.abbreviate(commitId, requestedLength);
        return Optional.of(abbreviatedObjectId);
      } catch (IOException e) {
        return Optional.empty();
      }
    }
docs: JGit won't ever use 1 char as abbreviated ID, that's why only values of:
  <ul>
  <li>0 (special meaning - don't show commit id at all),</li>
  <li>the range from 2 to 40 (inclusive) are valid</li>
  </ul>
  
  @return the abbreviated commit id, possibly longer than the requested len (if it wouldn't be unique)