Before this commit, when the start datetime of base_event_id in recurrences was not set, a traceback would occurs when trying to notify the user. closes odoo/odoo#71724 X-original-commit: d5b9403c0023d8df49487293b217c59265189a7a Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com> Signed-off-by: Arnaud Joset <arj-odoo@users.noreply.github.com>