Function to_query_string 

pub fn to_query_string<T>(value: &T) -> Result<Option<String>, Error>
where
    T: Serialize,

Serialize a query struct into a query string (no leading ?).

Returns None when the result is empty, so the caller can skip the ? entirely. Vec fields become repeated keys and None fields are omitted.

Errors

Returns the underlying serde_html_form error if value cannot be represented as a flat key/value list.