The command is fine. If you are testing the the expression using "Test" this will happen because there is no value attached to the columns. If you try this in the expression, it will work as the values are hardcoded and therefore able to be tested...
(new BigDecimal(3.0)).multiply((new BigDecimal(2.0)))
Don't worry about this so much. Just run the job if you want to test it with some actual data.