toJson method
Implementation
@override
Map<String, dynamic> toJson() => <String, dynamic>{
'currency': currency,
'amount': amount,
'star_count': starCount,
'discount_percentage': discountPercentage,
'month_count': monthCount,
'store_product_id': storeProductId,
'sticker': sticker?.toJson(),
'@type': constructor,
};