required field

[oo-work]

message SayRequest{
  required string str1 = 1;
  optional int32 int1 = 2;
}

When I use proto2's required and optional, the code generated by protoc --dart_out=grpc:lib/src/generated -Iprotos .\protos\* is as follows

class SayRequest extends $pb.GeneratedMessage {
  factory SayRequest({
    $core.String? str1,
    $core.int? int1,
  }) {
    final $result = create();
    if (str1 != null) {
      $result.str1 = str1;
    }
    if (int1 != null) {
      $result.int1 = int1;
    }
    return $result;
  }
  SayRequest._() : super();
}

All fields are optional, it does not follow the required as expected

factory SayRequest({
    required String str1,
    int? int1,
  })