Hi Pradeep,
The easiest way would be to configure the Data Proposal, and add a master record to propose the value 0,001, so that value would be automatically added whenever the system calculates to zero. It would be best to include the UoM in the proposal, so that you can set the minimum figure according to the unit - for example, anything measured in "pieces" would need a quantity of '1' (not 0,001).
By the way, it's unusual to find KG for the supplementary quantity. Which Tariff Code are you referring to?
Regards,
Dave