Symfony Messenger 4.3 - Consuming messages from doctrine transport fails (exception thrown)

Symfony version: 4.3.2

PHP: 7.2.20

I am trying to use the messenger component with the doctrine transport asynchronously. I have installed the messenger via composer require messenger with the help of Symfony Flex.

I have activated the doctrine transport by MESSENGER_TRANSPORT_DSN=doctrine://default in the .env.local.In the messenger config the transport is configured as well:

framework:    messenger:           transports:            async: '%env(MESSENGER_TRANSPORT_DSN)%'        routing:'App\Message\SomeNotification': async

When dispatching the message in the controller with $this->dispatchMessage(new SomeNotification('some content')); everything is fine. The table messenger_messages of the doctrine transport gets created automatically and the message is saved in the table correctly.

When trying to consume the message with ./bin/console messenger:consume async I'm getting the following error:

 [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       

So the $routableBus in the Symfony\Component\Messenger\Command\ConsumeMessagesCommand is empty which leads to the crash when instantiating the Worker.