docs: public List<E> pollBatch() {
  		lock.lock();
  		try {
  			if (open) {
  				if (elements.size() > 0) {
  					ArrayList<E> result = new ArrayList<>(elements);
  					elements.clear();
  					return result;
  				} else {
  					return null;
  				}
  			} else {
  				throw new IllegalStateException("queue is closed");
  			}
  		} finally {
  			lock.unlock();
  		}
  	}