code: public static final <K,V> MapList<K,V> unmodifiableMapList(MapList<K,V> map)
      {
          return new UnmodifiableMapList(Collections.unmodifiableMap(map), map.getComparator());
      }
docs: Returns unmodifiable MapList.
  @param <K>
  @param <V>
  @param map
  @return