immutable_or_is_it.dart

class IPromiseIAmImmutable {
  IPromiseIAmImmutable(this.field);
  
  final int? field;
}

class OhYeahWatchThis implements IPromiseIAmImmutable {
  int? _field;
  
  @override
  int? get field {
    _field = _field == null ? 1 : null;
    return _field;
  }
}

void main() {
  checkNotNull(IPromiseIAmImmutable(5));
  checkNotNull(IPromiseIAmImmutable(null));
  checkNotNull(OhYeahWatchThis());
}

void checkNotNull(IPromiseIAmImmutable object) {
  if (object.field != null) {
    print('object.field is not null. See for youself: ${object.field}');
  } else {
    print('object.field is null. See for youself: ${object.field}');
  }
}