Unnecessary Non-null assertion operator in Builder

[Nico04]

When using a default value instanciation, the build() method of the builder adds an unecessary "!", which may leads to a throw.
For instance with this class :

@JsonSerializable()
@DataClass(changeable: true, buildable: true)
class IbpMeasure extends WithArea with _$IbpMeasure {
 const IbpMeasure({
    required this.method,
    this.comments,
    String? version,
  }) : version = version ?? '3_0';
  factory IbpMeasure.fromJson(JsonObject json) => _$IbpMeasureFromJson(json);
  JsonObject toJson() => _$IbpMeasureToJson(this);

  final IbpMethod method;
  final String? comments;
  final String version;
}

The generated builder is :

IbpMeasure build() => IbpMeasure(
  method: method!,
  comments: comments,
  version: version!,
);

But for the version field, the "!" should be present at all, because in the constructor it's nullable.