Function assert_name_and_value 

fn assert_name_and_value<K, V>(name: K, value: V) -> (HeaderName, HeaderValue)
where
    HeaderName: TryFrom<K>,
    <HeaderName as TryFrom<K>>::Error: Into<Error>,
    HeaderValue: TryFrom<V>,
    <HeaderValue as TryFrom<V>>::Error: Into<Error>,