trait ServingErrorSender extends Sender{
 this: ServingError =>   // force to be mixed with a ServingError class, (look for 'see cake-pattern')  def send(): Unit = send(this)
 override def send(event: ServingError): Unit = ""
}

trait ServingError extends ServingErrorSender{
 val code: Int
 val description: String
 val content: String
}