Sum certain

§ 28:3—106. Sum certain (1) The sum payable is a sum certain even though it is to be paid (a) with stated interest or by stated installments; or (b) with stated different rates of interest before and after default or a specified date; or (c) with a stated discount or addition if paid before or after the date fixed for payment; or (d) with exchange or less exchange, whether at a fixed rate or at the current rate; or (e) with costs of collection or an attorney’s fee or both upon default... (2) Nothing in this section shall validate any term which is otherwise illegal.