flutter save api response to sqflite database causes error Invalid argument [Instance of 'Photo'] with type List

Question

I was trying to save from API call List of Pets which contain String values and Pets Image URL list but when I try to save to sqflite database I got an error

Invalid argument [Instance of 'Photo'] with type List.

response from postman looks like below

 "pets": [
        {
            "type": "Cat",
            "gender": "male",
            "size": "medium",
            "age": "baby",
            "photos": [
                {
                    "url": null
                }
            ],
            "good_with_children": true,
            "pet_id": "63fdb1b5cfaa63a48ed4a48e",
            "source": "local"
        },
]

here is my model

class PetsModel extends Pets{
  PetsModel(
      {
        required super.type,
        required super.gender,
        required super.size,
        required super.age,
        required super.photos,
        required super.good_with_children,
        required super.source});

  factory PetsModel.fromJson(Map<String, dynamic> json)=>
      PetsModel(type:json['type'],
          gender:json['gender'],
          size:json['size'],
          age:json['age'],
          photos:List<Photo>.from(json['photos'].map((x) => Photo.fromJson(x))),
          good_with_children:json['good_with_children'],
          source:json['source']);


          Map<String, dynamic> toJson() => {
            "type": type,
            "gender": gender,
            "size": size,
            "age": age,
            "photos": photos,
            "good_with_children": good_with_children,
            "source": source,
          };

Photos Model

class Photo {
  Photo({
    required this.url,
  });

  String? url;

  factory Photo.fromJson(Map<String, dynamic> json) => Photo(
    url: json["url"]??'',
  );


}

so I have create a sqlite database to store the response for offline usage and to save the value i used the following

createPets(PetsModel newPetsList) async {
    final db = await database;
    final res = await db!.insert('pets', newPetsList.toJson());
    return res;
  }

so the main cause of error is The Photo List and I have seen different solutions I couldn't solve it out. any help is appreciated