I have been following this tutrial to create my first symfony web application: link
And everything went well until I had to create event listeners.
I have followed the instructions as they are on the page but when I go to check that there are no errors I get the following error: The definition for "tags" has no class.
This is what I have in services.yaml:
App\EventListener\Author\CheckIsAuthorListener:
tags:
- { name: kernel.event_listener, event: kernel.controller }
And the rest of the files are the same as those in the tutorial. Does anyone know that it may be failing?