Predicate<T> predicate) {
    return new PredicateFunction<>(predicate);
  }

  /**
   * @see Functions#forPredicate
   */
  private static final class PredicateFunction<T extends @Nullable Object>
      implements Function<T, Boolean>, Serializable {
    private final Predicate<T> predicate;

    private PredicateFunction(Predicate<T> predicate) {
      this.predicate = checkNotNull(predicate);