Fix #3201
As far as previous_assignee_id is nil, User.find fails to find such an id. Substitute @previous_assignee with an empty User instance to avoid failure (in templates, too)
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
As far as previous_assignee_id is nil, User.find fails to find such an id. Substitute @previous_assignee with an empty User instance to avoid failure (in templates, too)