Not creating the .g.dart class in Flutter(Dart)

I have used the json_serializable library in flutter and created a class and created the Annotation of the library i.e. json_serializable in the class as below example:

import 'package:json_annotation/json_annotation.dart';
part 'AppData.g.dart';

@JsonSerializable()
class AppData {
  String? Username;
  String? Password;
  String? Avatar;
  String? Name;
  String? Family;
  String? FullName;
  String? UserType;
  String? Email;
  String? Mobile;

  AppData({this.Username, this.Password, this.Email,
    this.Family, this.Name, this.FullName, this.UserType, this.Mobile, this.Avatar})

  factory AppData.fromJson(Map<String, dynamic> json) =>
      _$AppDataFromJson(json);

  Map<String, dynamic> toJson() => _$AppDataToJson(this);
}

The problem is that when I type dart run build_runner build -d in the terminal, it gives an error and does not create the AppData.g.dart class.

The error image it gives in the terminal:

You are missing a semicolon to close the AppData constructor: AppData({this.Username, this.Password, this.Email,this.Family, this.Name, this.FullName, this.UserType, this.Mobile, this.Avatar});