Hey, when do checkboxes return null ? nlapiGetLineItemValue("item","custcol_wb_sent_on_edi",1); custcol_wb_sent_on_edi is checkbox field newly added. It should return  'F' when unchecked. but I am getting null instead (edited)  Same is happening with a list record field , It should return "" when not selected. What I am missing ?

AFAIK if it's never been set then it's blank, if it's flip-flopped between set/unset then you'd see T / F (or true/false in SS2.0) To be safe I would make any checks against it being/not being "T".