code: @SuppressWarnings({ "unchecked", "cast" })
      public static <K, V> MapFieldLite<K, V> emptyMapField() {
          return (MapFieldLite<K, V>) EMPTY_MAP_FIELD;
      }
docs: Returns an singleton immutable empty MapFieldLite instance.
  
  @param <K> the key type
  @param <V> the value type
  @return the map field lite