I have an externally defined XML standard I'm trying to write to which includes requiring empty attribute values. As an example, I need to write the following:

<TIM A="" D="4">

Where my A attribute needs to be written with an empty value, and D needs a constant value. Is it possible to achieve this with the crate using the serde serialize feature? Ideally, I'd like to use an Option like this:

#[derive(Serialize, Debug)]
struct Tim {
   a: Option<String>,
   b: u8,
}

But when I do that, and set a to None, the A attribute isn't serialized at all. I'm not sure that the crate would be able to decide whether or not to serialize the attribute, so I'm guessing I'll need serialize_with. Also tried that, but haven't been able to get it to write out an empty attribute value. The closest I've gotten is writing out <TIM A=" " D="4"/> but in my case, the space in the A attribute value is invalid.