docs: public static ArrayList<ClassLabel> allClassLabels(MultipleObjectsBundle bundle, int col) {
      HashSet<ClassLabel> labels = new HashSet<ClassLabel>();
      for(int i = 0, l = bundle.dataLength(); i < l; ++i) {
        Object o = bundle.data(i, col);
        if(o == null || !(o instanceof ClassLabel)) {
          continue;
        }
        labels.add((ClassLabel) o);
      }
      ArrayList<ClassLabel> ret = new ArrayList<>(labels);
      Collections.sort(ret);
      return ret;
    }