code: @SuppressWarnings("unchecked")
  	@Nullable
  	public static <T> QueueSubscription<T> as(Subscription s) {
  		if (s instanceof QueueSubscription) {
  			return (QueueSubscription<T>) s;
  		}
  		return null;
  	}
docs: Returns the subscription as QueueSubscription if possible or null.
  @param <T> the value type of the QueueSubscription.
  @param s the source subscription to try to convert.
  @return the QueueSubscription instance or null