unpaidInvoiceOf method

Implementation

UHotelInvoiceResponse? unpaidInvoiceOf(UHotelReservationResponse i) {
  final List<UHotelInvoiceResponse> invoices = i.invoices ?? <UHotelInvoiceResponse>[];
  for (final UHotelInvoiceResponse inv in invoices) {
    if (!inv.isPaid) return inv;
  }
  return null;
}