public SupportSlot AddSlot(SupportEngineer engeneer)
        {
            if (IsFilled)
            {
                throw new InvalidOperationException();
            }

            var supportSlot = new SupportSlot
            {
                Engeneer = engeneer,
                Date     = _date
            };

            _slots.Add(supportSlot);
            return(supportSlot);
        }
 public void AddSupportSlot(SupportSlot slot)
 {
     _slots.Add(slot);
 }