Empty sasl.username disables sasl.authentication

[katin-dev]

I found it very convenient to disable sasl authentication on dev machine by simple setting sasl.username into empty string.

So I have messenger config like so:

framework:
    messenger:
        reset_on_message: true
        transports:
          dsp:
              dsn: 'kafka://%env(DSP_KAFKA_HOSTS)%'
              options:
                  topic:
                      name: "%env(DSP_KAFKA_TOPIC_NAME)%"
                  kafka_conf:
                      security.protocol: 'sasl_plaintext'
                      sasl.mechanisms: 'SCRAM-SHA-256'
                      sasl.username: '%env(DSP_KAFKA_USERNAME)%'
                      sasl.password: '%env(DSP_KAFKA_PASSWORD)%'

On production server i have non-empty DSP_KAFKA_USERNAME but on local dev machine DSP_KAFKA_USERNAME='' and there is only one messenger.yaml