Empty strings not correctly deserialized

[JonathanBrouwer]

The following example fails:

#[derive(YaSerialize, YaDeserialize)]
pub struct Test {
    v: String
}

#[test]
fn test() {
    let v = Test {
        v: "".to_string()
    };

    yaserde::de::from_str::<Test>(&dbg!(yaserde::ser::to_string(&v).unwrap())).unwrap();
}

The struct is correctly serialized to:

<?xml version=\"1.0\" encoding=\"utf-8\"?><Test><v></v></Test>

The error message is "v is a required field of Test". The problem occurs because the visit_str function is not called since there is no string.

[MarcAntoine-Arnaud]

In fact xml-rs does not handle event XmlEvent::Characters.

So only a StartElement and EndElement are emitted.

So specific code has to be done for that case, without breaking the rest :P