code: protected static NumberValue multiply(NumberValue multiplicand, NumberValue multiplier) {
          if (multiplicand==null) {
              throw new ArithmeticException("The multiplicand cannot be null");
          }
          if (multiplier==null) {
              throw new ArithmeticException("The multiplier cannot be null");
          }
          return new DefaultNumberValue(
                  multiplicand.numberValueExact(BigDecimal.class).multiply(multiplier.numberValue(BigDecimal.class)));
      }
docs: A protected helper method to multiply 2 {@link NumberValue} types.<br>
  If either of the values is <code>null</code> an {@link ArithmeticException} is thrown.
  
  @param multiplicand the first value to be multiplied
  @param multiplier   the second value to be multiplied
  @return the result of the multiplication as {@link NumberValue}