Dependency on a non-existent service "app.repository.user_repository"

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Using Symfony 4, I'm setting up password grant handling following these suggestions. When I make a call to /token, I get the following error:

The service "App\EventListener\UserResolveListener" has a dependency on a non-existent service "app.repository.user_repository".

which relates to the arguments section in services.yaml:

App\EventListener\UserResolveListener:
    arguments:
        - '@app.repository.user_repository'

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Solution was to simply remove the arguments key from services.yaml.