if ret.Signature() != "v" {
            writing = append(writing, jen.If(jen.Err().Op("=").Add(v.Type.Marshal(v.Name, "&buf")).Op(";").Err().Op("!=").Nil()).Block(
                jen.Id(`return ret, fmt.Errorf("serialize `+v.Name+`: %s", err)`),
            ))
        } else {