Field help (UPDNULPRI) 

The Update zero price check box only applies to grouped price lists where the Price processing is set to 'Value' or 'Coefficient'.

When the box is checked, the system forces the gross price of the list on product lines with a null gross price. Contrary to the usual logic of grouped price lists, the null price will not be considered as the best price.

This rule is the same when the price set up for the grouped price list (Price field in the Price lists entry function) is null: a null value (price, discount or charge) never replaces the entered line value, whether the Update zero price check box is selected or not.

For other grouped price lists, the process remains the following (Update zero price box selected or not):