Simplicio
you are right . i dont have nulls but have some blanks that causing this issue.
i changed to following and it worked beautifully
SELECT * FROM it WHERE
(!EMPTY(code) AND INLIST(ALLTRIM(code),'PT01','PT02','PT03','PT04')) OR
(!EMPTY(usercode) AND INLIST(ALLTRIM(usercode),'PT01','PT02','PT03','PT04'))

Thanks for ur help