Function none_as_empty_string 

pub fn none_as_empty_string<T: Serialize, S>(
    value: &Option<T>,
    serializer: S,
) -> Result<S::Ok, S::Error>
where
    S: Serializer,

Serde serializiation decorator to map None to an empty String, and forward Somes to the Serialize implementation for T.

To be used like this: #[serde(serialize_with = "empty_string_as_none")]