code: func (b *Broker) AdjustRoutingKey(s *tasks.Signature) {
  	if s.RoutingKey != "" {
  		return
  	}
  
  	s.RoutingKey = b.GetConfig().DefaultQueue
  }
docs: // AdjustRoutingKey makes sure the routing key is correct.
  // If the routing key is an empty string:
  // a) set it to binding key for direct exchange type
  // b) set it to default queue name