code: public List<? extends Element> getMemberList(Character index) {
          SortedSet<Element> set = indexmap.get(index);
          if (set == null)
              return null;
          List<Element> out = new ArrayList<>();
          out.addAll(set);
          return out;
      }
docs: Return the sorted list of members, for passed Unicode Character.
  
  @param index index Unicode character.
  @return List member list for specific Unicode character.