What's the syntax for CONTAINER_EXPIRATION_POLICY_ATTRIBUTES ? #2284

I'm trying to figure out the syntax for the gitlab cli to set the container expiration policy attributes for my projects.

gitlab project update --id <ID> --container-expiration-policy-attributes CONTAINER_EXPIRATION_POLICY_ATTRIBUTES.

I've tried yaml syntax, python syntax, even writing the data in a file and reading it back with @/tmp/filename.
Each of my attempts resulted in 'Impossible to update object (400: container_expiration_policy_attributes is invalid)'

Does anyone know the correct syntax to set the policy attributes per CLI ?
It was easy to do with the gitlab python module, but I'm sure that I could accomplish the same with the CLI.