Function json 

pub fn json<T, I>(paths: I) -> Result<Option<T>, Error>
where
    T: for<'de> Deserialize<'de> + Merge,
    I: IntoIterator<Item = PathBuf>,

Available on crate features file and json only.

Evaluate paths using File and the Json format.

This is a convenience function and does no magic. Returns Ok(None) only if paths is empty.