The methods `get_work_hours_count` and `_attendance_intervals` raise a traceback if `self` does not contain a single calendar record. This commit adds an explicit check for this requirement. Related PR odoo/enterprise#10593 closes odoo/odoo#51326 X-original-commit: e5d93be382b03c7a9c925b4a2e6be6875843195d Related: odoo/enterprise#10619 Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>