Feature request: Support for a blank implementation for unit variant(s) of an enum

Consider...

#[derive(Deserialize, Serialize, Debug)]
#[serde(tag = "event")]
pub enum Event<'a> {
    GameSessionEnded(#[serde(borrow)] GameSessionEnded<'a>),
    PlayerSessionEnded(#[serde(borrow)] PlayerSessionEnded<'a>),
    EncounterEnded(#[serde(borrow)] EncounterEnded<'a>),
    PlayerEncounterEnded(#[serde(borrow)] PlayerEncounterEnded<'a>),
    ....

    #[serde(other)]
    Unknown,
}

Would be like to have a null implementation for Unknown