toJson method
Send any Object or Object List such as a product or productList to json String
Implementation
Future<String> toJson(dynamic T) async {
if (T is List) {
final list = <dynamic>[];
for (var o in T) {
list.add(await o.toMap());
}
return json.encode(list);
} else {
return json.encode(await T.toMap());
}
}