internal new void Add(IGatewayShipMethod item)
        {
            using (new WriteLock(_addLocker))
            {
                if (Contains(GetKeyForItem(item)))
                {
                    return;
                }

                base.Add(item);
            }
        }
 protected override Guid GetKeyForItem(IGatewayShipMethod item)
 {
     return(item.ShipMethod.Key);
 }