/**
  * Default handler for a consumer which simply add it to the MAV using {@link
  * ConsumerAbstractController#CONSUMER_ID_KEY}
  *
  * @param mav
  * @param consumer
  * @throws IllegalArgumentException if consumer is null
  */
 protected void handleConsumer(ModelAndView mav, EventConsumer consumer)
     throws IllegalArgumentException {
   if (consumer == null) {
     throw new IllegalArgumentException(
         "ERROR: Consumer instance '" + consumer.getId() + "' not found");
   }
   mav.addObject(CONSUMER_ID_KEY, consumer);
 }