private void RecalculateCost() { if (ProductLines.Count == 0) { CustomMessageBox.ShowError("Please, specify at least one product line"); return; } double?distance = _addressResolver.GetDistanceTo(_delivery.Destination); if (distance == null) { CustomMessageBox.ShowError("Address is not found"); return; } _delivery.RecalculateCostEstimate(distance.Value); Notify(nameof(CostEstimate)); }