Go on Timeoff > Configuration > Accrual Plans
Before this commit, when no rules were set, there was no visual feedback.
This was because that feedback only appeared when the form view was in readonly,
which is virtually never the case now because of the always edit feature.
After this commit, there is the relevant visual message if no rule is set.
X-original-commit: 599554adc3883fa2742764d8f948258dee2ef89e
Part-of: odoo/odoo#102578