None values serialize as empty element and fail round trip deserializing

[hfiguiere]

#[derive(Clone, Debug, Default, Deserialize, PartialEq, Serialize)]
#[serde(rename = "results")]
pub struct Results {
    #[serde(default)]
    pub raw_type_id: Option<u32>,
}

let r = Results { raw_type_id: None };

Serializing r will output:

<results>
<raw_type_id />
</results>

Deserializing the xml will fail with:

thread 'tests::deser' panicked at 'deserialize: InvalidInt(ParseIntError { kind: Empty })', src/lib.rs:133:45

So round trip serialization fails.

However

<results>
</results>

Will be sucessful and equal to

Results { raw_type_id: None }

Note: serde_xml_rs has similar issues.

I have two expectations here:

1. that None value be allowed to not generate an empty element. This would work around the serialization error.
2. the an empty element desrialization works for the underlying type is Option<> and then yield None.

Unless I'm misunderstanding how this is supposed to work, but round trip defintely fails.

[hfiguiere]

Probably the same as #497

[Mingun]

Yes, this is duplicate of #497