/// If a payment_secret *is* provided, we assume that the invoice had the payment_secret feature
/// bit set (either as required or as available). If multiple paths are present in the Route,
/// we assume the invoice had the basic_mpp feature set.
/// If a payment_secret *is* provided, we assume that the invoice had the payment_secret feature
/// bit set (either as required or as available). If multiple paths are present in the Route,
/// we assume the invoice had the basic_mpp feature set.