toJson method
Creates a json from the object
Implementation
Map toJson() {
return {
'id': id,
'from': from,
'currency': currency,
'total_amount': totalAmount,
'invoice_payload': invoicePayload,
'shipping_option_id': shippingOptionId,
'order_info': orderInfo,
}..removeWhere((_, v) => v == null);
}