[update] many2one res.partner

models/calendar.py

@@ -33,6 +33,7 @@ class CGScopCalendar(models.Model):
         comodel_name='res.partner',
         string='Contact',
         domain=[('is_company', '=', 'True')],
+        ondelete='set null',
         default=_default_coop_id)
     project_id = fields.Many2one(
         comodel_name="project.project",