code: public <U extends UnsortedGrouping<?>> void add(int id, U set) {
  		cacheSetType(id, SetType.UNSORTED_GROUPING);
  		unsortedGroupings.put(id, set);
  	}
docs: Adds the given {@link UnsortedGrouping} to this cache for the given ID.
  
  @param id  Set ID
  @param set UnsortedGrouping to add
  @param <U> UnsortedGrouping class