@SuppressWarnings({"unchecked", "rawtypes"})
      // immutable collections are safe for covariant casts
      // and getting the generics right for EnumMap is difficult to impossible
      ImmutableMap<K, V> result = ImmutableEnumMap.asImmutable(new EnumMap(enumMap));
      return result;
    }

    int size = map.size();
    switch (size) {
      case 0:
        return of();
      case 1: