passing Null value to crystal report selection formula.

hi erverybody,

here is my selection formula

{MOH_EMPLOYEE_DETAILS.DEP_CODE}='' and {MOH_EMPLOYEE_DETAILS.SECTION_CODE}='' and {MOH_EMPLOYEE_DETAILS.DG_CODE}= '1132010000' and {MOH_EMPLOYEE_DETAILS.EMPLOYEE_NUMBER}='123' and {T_SHIFT_DETAILS.DATE_FROM} in date (2012,01,01) to date (2012,12,12))

i am passing some null value , but that dose not work with me

i tried this also

isNull({MOH_EMPLOYEE_DETAILS.DEP_CODE}) and isNull({MOH_EMPLOYEE_DETAILS.SECTION_CODE}) and {MOH_EMPLOYEE_DETAILS.DG_CODE}= '1132010000' and {MOH_EMPLOYEE_DETAILS.EMPLOYEE_NUMBER}='123' and {T_SHIFT_DETAILS.DATE_FROM} in date (2012,01,01) to date (2012,12,12))

but still it is not working with me

can any one help me please.

regards,