Log-forward without listener?

I try to figure out how I can use the quite new function of log-forward released in version 2.3.
Because on one location I only need to balance syslog messages and do nothing else, I tried to create a cfg file only with some log-forward parts.
But haproxy is not loading because the listener is missing.
If I check the docs it always looks like log-forward can be used without anything else.
But it seems I’m on a wrong way.
If I add a listen section with some random config all is loaded and I see that my syslog destination port is up on the host.

Thanks for any help!