ImmutableBiMap.Builder::buildOrThrow,
        new Collector.Characteristics[0]);
  }

  static <T extends @Nullable Object, K extends Enum<K>, V>
      Collector<T, ?, ImmutableMap<K, V>> toImmutableEnumMap(
          Function<? super T, ? extends K> keyFunction,
          Function<? super T, ? extends V> valueFunction) {
    checkNotNull(keyFunction);
    checkNotNull(valueFunction);
    return Collector.of(