How to serializing Option<String> to self close element with #[serde(rename = "$unflatten={}")]

[LokiSharp]

I want to serialize a Option<String> to unflatten self close element like <Foo><option-with-none-value/></Foo>. Is there any way to control it?

Code:

#[derive(Debug, Deserialize, Serialize, PartialEq)]
pub struct Foo {
    #[serde(rename = "$unflatten=option-with-none-value")]
    pub body: Option<String>,
}

to_string(&Foo { body: None }).unwrap()

Result:

<Foo><option-with-none-value></option-with-none-value></Foo>

[Mingun]

In current master this is how it works out-of-box since #490 is merged:

#[derive(Debug, Deserialize, Serialize, PartialEq)]
pub struct Foo {
    #[serde(rename = "option-with-none-value")]
    pub body: Option<String>,
}

assert_eq!(
    to_string(&Foo { body: None }).unwrap(),
    "<Foo><option-with-none-value/></Foo>"
);

But deserialization of that value will return Some("") for now due to #497.