}

  private static final class EmptySetBuilderImpl<E> extends SetBuilderImpl<E> {
    private static final EmptySetBuilderImpl<Object> INSTANCE = new EmptySetBuilderImpl<>();

    @SuppressWarnings("unchecked")
    static <E> SetBuilderImpl<E> instance() {
      return (SetBuilderImpl<E>) INSTANCE;
    }

    private EmptySetBuilderImpl() {
      super(0);
    }

    @Override