Unhandled Exception: NoSuchMethodError: The method '[]' was called on null. while parsing-CodePudding

i have a json object that includes an object that could be null. here is my json:

I/flutter (23570): ║    {
I/flutter (23570): ║         elements: [
I/flutter (23570): ║            {
I/flutter (23570): ║                 id: 1,
I/flutter (23570): ║                 name: "a1",
I/flutter (23570): ║                 owner: {firstName: امین, lastName: جمالی, mobile: 9014523821}
I/flutter (23570): ║            },
I/flutter (23570): ║          {id: 2, name: a2}
I/flutter (23570): ║         ],
I/flutter (23570): ║         totalElements: 2
I/flutter (23570): ║    }

owner filed in first element has data and in second one is empty. here is my view model:

class UnitItemViewModel {


final int id;
  final String name;
  UnitOwner? owner;

  UnitItemViewModel({
    required this.id,
    required this.name,
    this.owner,
  });

  factory UnitItemViewModel.fromJson(final Map<String, dynamic> json) =>
      UnitItemViewModel(
        id: json['id'],
        name: json['name'],
        owner: UnitOwner.fromJson(json['owner']),
      );
}
class UnitOwner {


final String firstName, lastName;
  final String mobile;

  UnitOwner({
    required this.firstName,
    required this.lastName,
    required this.mobile,
  });

  factory UnitOwner.fromJson(final Map<String, dynamic> json) => UnitOwner(
        firstName: json['firstName'],
        lastName: json['lastName'],
        mobile: json['mobile'],
      );
}

while parsing i got this exception:

E/flutter (23570): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: 

NoSuchMethodError: The method '[]' was called on null.
E/flutter (23570): Receiver: null
E/flutter (23570): Tried calling: []("firstName")

and here is my repository:

final items = (data['elements'] as List)
        .map((final e) => UnitItemViewModel.fromJson(
              e as Map<String, dynamic>,
            ))
        .toList();

any idea will be great.

CodePudding user response：

This line you get error because json is null

firstName: json['firstName']

You should change this fromJson function like this :

factory UnitOwner.fromJson(final Map<String, dynamic>? json) => UnitOwner(
        firstName: json?['firstName'] ?? '',
        lastName: json?['lastName'] ?? '',
        mobile: json?['mobile'] ?? '',
      );