code: public function getMessage($id = null)
      {
          if (!is_null($id)) {
              return array_key_exists($id, $this->messages) ? $this->messages[$id] : null;
          } elseif (count($this->messages)>0) {
              return current($this->messages);
          } else {
              $message_class = $this->getDefault('messager');
              if (class_exists($message_class)) {
                  $this->addMessage(new $message_class);
                  return current($this->messages);
              } else {
                  throw new \Exception(
                      sprintf('Default message class "%s" not found!', $message_class)
                  );
              }
          }
      }
docs: Get a message by id or current message
  
  If no message exists for now, it will be created using the default `messager` class.
  
  @param   int $id
  @return string
  @throws \Exception if the default `messager` class doesn't exist