Function optional
pub fn optional<S: Serializer>(duration: &Option<SignedDuration>, se: S) -> Result<S::Ok, S::Error>Serialize an optional SignedDuration in the friendly
duration format using compact designators.
optionalpub fn optional<S: Serializer>(duration: &Option<SignedDuration>, se: S) -> Result<S::Ok, S::Error>Serialize an optional SignedDuration in the friendly
duration format using compact designators.