Macro print_maybe_json

macro_rules! print_maybe_json {
    (
        $json_printer:expr, $($val:expr),* => force_quotes
    ) => { ... };
    (
        $json_printer:expr, $($val:expr),*
    ) => { ... };
    (
        $json_printer:expr, $($val:expr),* => $force_quotes:expr
    ) => { ... };
}