docs: public static <E> CloseableIterator<E> iterator(Publisher<E> publisher, int fetchSize) {
        // This iterator from rxjava2 implements Disposable akin to Closeable
        Iterator<E> iterator = Flowable.fromPublisher(publisher).blockingIterable(fetchSize).iterator();
        return new CloseableIterator<E>() {
           @Override
           public void close() {
              ((Disposable) iterator).dispose();
           }
  
           @Override
           public boolean hasNext() {
              return iterator.hasNext();
           }
  
           @Override
           public E next() {
              return iterator.next();
           }
        };
     }