dart null safety class initialization - flutter

Question

I built two classes.
first class is the video Class.
second class is Player Class.
And one of Player variables is list of video class
and after dart null safety it is not allowed to add null varaiables
I should add initialization value to the class ( I don't want to add required ).
First Class - Video
import 'dart:convert';
VideoModel videoModelFromJson(String str) =>
VideoModel.fromJson(json.decode(str));
String videoModelToJson(VideoModel data) => json.encode(data.toJson());
class VideoModel {
VideoModel({
this.playerVideoId = -1,
this.playerIdId = -1,
this.videoLink = "Please Upload",
});
int playerVideoId;
int playerIdId;
String videoLink;
factory VideoModel.fromJson(Map<String, dynamic> json) => VideoModel(
playerVideoId: json["playerVideoId"],
playerIdId: json["playerId_id"],
videoLink: json["videoLink"],
);
Map<String, dynamic> toJson() => {
"playerVideoId": playerVideoId,
"playerId_id": playerIdId,
"videoLink": videoLink,
};
}
Second Class which contain error in defining videos
// To parse this JSON data, do
//
// final playerBasic = playerBasicFromJson(jsonString);
import 'dart:convert';
import 'package:sportive/pages/player/Model/Video_Model.dart';
PlayerBasic playerBasicFromJson(String str) =>
PlayerBasic.fromJson(json.decode(str));
String playerBasicToJson(PlayerBasic data) => json.encode(data.toJson());
class PlayerBasic {
PlayerBasic({
this.playerId = -1,
this.userIdId = -1,
this.playerFirstName = "",
this.playerLastName = "",
this.nationality = "",
this.birthday = "",
this.height = -1,
this.weight = -1,
this.currentCountry = "",
this.currentCity = "",
this.game = "",
this.image = "",
this.gender = "Male",
this.videos, // Error here Parameter The parameter 'videos' can't have a value of 'null' because of its type, but the implicit default value is 'null'.
//Try adding either an explicit non-'null' default value or the 'required' modifier
});
int playerId;
int userIdId;
String playerFirstName;
String playerLastName;
String nationality;
String birthday;
int height;
int weight;
String currentCountry;
String currentCity;
String game;
String image;
String gender;
List<VideoModel> videos;
factory PlayerBasic.fromJson(Map<String, dynamic> json) => PlayerBasic(
playerId: json["playerId"],
userIdId: json["userId_id"],
playerFirstName: json["playerFirstName"],
playerLastName: json["playerLastName"],
nationality: json["nationality"],
birthday: json["birthday"],
height: json["height"],
weight: json["weight"],
currentCountry: json["currentCountry"],
currentCity: json["currentCity"],
game: json["game"],
image: json["image"],
gender: json['gender'],
videos: json['videos'],
);
Map<String, dynamic> toJson() => {
"playerId": playerId,
"userId_id": userIdId,
"playerFirstName": playerFirstName,
"playerLastName": playerLastName,
"nationality": nationality,
"birthday": birthday,
"height": height,
"weight": weight,
"currentCountry": currentCountry,
"currentCity": currentCity,
"game": game,
"image": image,
"gender": gender,
"videos": videos,
};
}
Sorry Iam Flutter beginner question.

Answer 1

Just change the videos declaration to
List<VideoModel>? videos;
Let's suppose you have this class and you want to provide a default value for bar in the constructor:
class Foo {
List<int> bar;
}
If you want to be able to modify bar later:
class Foo {
// Use this
Foo({List<int>? bar}) : bar = bar ?? [];
List<int> bar;
}
void main() {
Foo foo;
foo = Foo();
print(foo.bar);
// Outputs []
foo.bar.add(4);
print(foo.bar);
// Outputs [4]
foo = Foo(bar: [1, 2, 3]);
print(foo.bar);
// Outputs [1, 2, 3]
foo.bar.add(4);
print(foo.bar);
// Outputs [1, 2, 3, 4]
}
If you want to keep bar immutable (i.e. you won't use methods such as add or remove):
class Foo {
// Use this
Foo({this.bar = const []});
List<int> bar;
}
void main() {
Foo foo;
foo = Foo();
print(foo.bar);
// Outputs []
// foo.bar.add(4);
// It'll throw Uncaught Error: Unsupported operation: add
foo = Foo(bar: [1, 2, 3]);
print(foo.bar);
// Outputs [1, 2, 3]
foo.bar.add(4);
print(foo.bar);
// Outputs [1, 2, 3, 4]
}