// Rollback rolls back the provided transaction (if err is non-nil) and wraps
// the error, if any, of the rollback into a RollbackError.
//
// The err parameter must be non-nil.
//
//   err = sa.Rollback(tx, err)
func Rollback(tx *gorp.Transaction, err error) error {
	return &RollbackError{
		Err:         err,
		RollbackErr: tx.Rollback(),
	}
}