code: public static <K, V, T extends Comparable<? super T>> AbstractGroupExpression<Pair<K, V>, SortedMap<T, V>> sortedMap(GroupExpression<K, T> key,
                                                                                                                           Expression<V> value) {
          return sortedMap(key, new GOne<V>(value));
      }
docs: Create a new aggregating map expression using a backing TreeMap
  
  @param key key for the map entries
  @param value value for the map entries
  @return wrapper expression