pub fn serialize<S: Serializer>(

        duration: &TimeDelta,

        serializer: S,

    ) -> Result<S::Ok, S::Error> {

        duration.num_seconds().serialize(serializer)

    }

    pub fn deserialize<'de, D: Deserializer<'de>>(deserializer: D) -> Result<TimeDelta, D::Error> {

        let secs = i64::deserialize(deserializer)?;

        TimeDelta::try_seconds(secs).ok_or_else(|| Error::custom("duration out of range"))

    }

    pub fn serialize<S: Serializer>(

        duration: &Option<TimeDelta>,

        serializer: S,

    ) -> Result<S::Ok, S::Error> {

        duration.map(|d| d.num_seconds()).serialize(serializer)

    }

    pub fn deserialize<'de, D: Deserializer<'de>>(

        deserializer: D,

    ) -> Result<Option<TimeDelta>, D::Error> {

        let secs = Option::<i64>::deserialize(deserializer)?;

        secs.map(|secs| {

            TimeDelta::try_seconds(secs).ok_or_else(|| Error::custom("duration out of range"))

        })

        .transpose()

    }