* @return function that returns {@code map.get(a)} when {@code a} is a key, or {@code
   *     defaultValue} otherwise
   */
  public static <K extends @Nullable Object, V extends @Nullable Object> Function<K, V> forMap(
      Map<K, ? extends V> map, @ParametricNullness V defaultValue) {
    return new ForMapWithDefault<>(map, defaultValue);
  }

   * @return function that returns {@code map.get(a)} when {@code a} is a key, or {@code
   *     defaultValue} otherwise
   */
  public static <K extends @Nullable Object, V extends @Nullable Object> Function<K, V> forMap(
      Map<K, ? extends V> map, @ParametricNullness V defaultValue) {
    return new ForMapWithDefault<>(map, defaultValue);
  }