title: Symfony Messenger 4.3 - Consuming messages from doctrine transport fails (exception thrown)
body: <p>Symfony version: <code>4.3.2</code></p>
  
  <p>PHP: <code>7.2.20</code></p>
  
  <p>I am trying to use the messenger component with the doctrine transport asynchronously. I have installed the messenger via <code>composer require messenger</code> with the help of Symfony Flex.</p>
  
  <p>I have activated the doctrine transport by <code>MESSENGER_TRANSPORT_DSN=doctrine://default</code> in the <code>.env.local</code>.
  In the messenger config the transport is configured as well:</p>
  
  <pre><code>framework:
      messenger:   
          transports:
              async: '%env(MESSENGER_TRANSPORT_DSN)%'
          routing:
              'App\Message\SomeNotification': async
  </code></pre>
  
  <p>When dispatching the message in the controller with <code>$this-&gt;dispatchMessage(new SomeNotification('some content'));</code> everything is fine. The table <code>messenger_messages</code> of the doctrine transport gets created automatically and the message is saved in the table correctly.</p>
  
  <p>When trying to consume the message with <code>./bin/console messenger:consume async</code> I'm getting the following error:</p>
  
  <pre><code> [Symfony\Component\Debug\Exception\FatalThrowableError]                                                                                                                                                                                                               
    Argument 2 passed to Symfony\Component\Messenger\Worker::__construct() must implement interface Symfony\Component\Messenger\MessageBusInterface, string given, called in ..../vendor/symfony/messenger/  
    Command/ConsumeMessagesCommand.php on line 190       
  </code></pre>
  
  <p>So the $routableBus in the <code>Symfony\Component\Messenger\Command\ConsumeMessagesCommand</code> is empty which leads to the crash when instantiating the Worker.</p>