code: public static SubscribeRequest createSubscribeReq(SubscribeElement el) {
  		if (el == null) {
  			throw new NullPointerException("el is not allowed to be null");
  		}
  
  		SubscribeRequest ret = createSubscribeReq();
  		ret.addSubscribeElement(el);
  		return ret;
  	}
docs: Create a {@link SubscribeRequest} with one {@link SubscribeElement}.
  
  @param el the {@link SubscribeElement} that is added to the new
  {@link SubscribeRequest}. This can either be {@link SubscribeUpdate} or
  {@link SubscribeDelete}.
  
  @return the new {@link SubscribeRequest}