Step 1 - Read with defaults

String readString(Map<String, dynamic> json, String key, [String fallback = '']) {
  final v = json[key];
  if (v is String) return v;
  return fallback;
}

int? readInt(Map<String, dynamic> json, String key) {
  final v = json[key];
  if (v is int) return v;
  if (v is num) return v.toInt();
  return null;
}

Step 2 - Result or exceptions at the model boundary

Use readString from step 1 in the same file.

class User {
  final String id;
  final String name;
  User({required this.id, required this.name});
}

class Result<T> {
  final T? value;
  final String? error;
  const Result.ok(this.value) : error = null;
  const Result.err(this.error) : value = null;
  bool get isOk => error == null;
}

Result<User> userFromJsonSafe(Map<String, dynamic> json) {
  final id = readString(json, 'id');
  final name = readString(json, 'name');
  if (id.isEmpty) return const Result.err('missing id');
  if (name.isEmpty) return const Result.err('missing name');
  return Result.ok(User(id: id, name: name));
}

Step 3 - Type mismatch

• If the API sends "id": 1 but you want String, convert explicitly: json['id'].toString() when id is num.

Good habit

• One function owns parsing for each model; callers get User or a clear error, not raw maps.

Practice tasks

• Implement readBool accepting true/false, 1/0, "yes"/"no".
• Return Result<Todo> when title is missing or not a string.