Function rs_es::json::serialize_map_optional_kv

pub fn serialize_map_optional_kv<S, K, V>(
    map_ser: &mut S, 
    key: K, 
    value: &Option<V>
) -> Result<(), S::Error> where
    S: SerializeMap,
    K: Serialize,
    V: Serialize, 

Useful serialization functions