toJson method
Implementation
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = <String, dynamic>{};
data['user_id'] = userId;
data['user_login'] = userLogin;
data['user_name'] = userName;
data['rank'] = rank;
data['score'] = score;
data.removeWhere((key, value) => value == null);
return data;
}