}
    Set<E> delegate = delegateOrNull();
    return (delegate != null)
        ? delegate.spliterator()
        : Spliterators.spliterator(
            requireElements(), 0, size, Spliterator.DISTINCT | Spliterator.ORDERED);
  }

  @Override
  public void forEach(Consumer<? super E> action) {
    checkNotNull(action);
    Set<E> delegate = delegateOrNull();
    if (delegate != null) {

  }

  @Override
  public boolean containsKey(@Nullable Object key) {
    Map<K, V> delegate = delegateOrNull();
    return (delegate != null) ? delegate.containsKey(key) : indexOf(key) != -1;
  }

  @Override
  public @Nullable V get(@Nullable Object key) {
    Map<K, V> delegate = delegateOrNull();
    if (delegate != null) {
      return delegate.get(key);
    }
    int index = indexOf(key);