mutable_state.rs

// mutable state
let mut sql_type = None;
let mut sql_type_ref = None;
if !type_args.is_empty() {
    sql_type = Some(quote!((#(#type_args),*)));
    sql_type_ref = Some(quote!((#(&'a #type_args),*)));
}

repetition.rs

// repetition
let sql_type = if type_args.is_empty() {
    None
} else {
    Some(quote!((#(#type_args),*)))
};

let sql_type_ref = if type_args.is_empty() {
    None
} else {
    Some(quote!((#(&'a #type_args),*)))
}

tuple_assignment.rs

// tuple assignment
let (sql_type, sql_type_ref) = if type_args.is_empty() {
    (None, None)
} else {
    (
        Some(quote!((#(#type_args),*))),
        Some(quote!((#(&'a #type_args),*))),
    )
};