Order constructor
Order({})
Implementation
Order({
required this.orderId,
required this.customerId,
required List<OrderItem> items,
this.subscription,
required this.timeSlot,
required this.createdAt,
}) : items = List.unmodifiable(items),
_status = OrderStatus.created {
if (items.isEmpty) {
throw ArgumentError("Order must contain at least one item");
}
}