Need Help on tackling null values in Filter

Hi ,

I am using below codes in Filter.

filter:if(isnull(local!empType),{},a!queryFilter(
field: "emptype",
operator: "=",
value: local!empType
))

It is displaying the error as  "Could not display interface. Please check definition and inputs. Interface Definition: Expression evaluation error at function a!gridField [line 37]: Expression evaluation error at function a!queryEntity [line 38]: Cannot apply a filter with a blank field name."

This is working fine when I am using ri!empType with some default value. But I do not want to use Rule input as I need to use this Interface in report.

Could someone please help me on this?

Thanks

Faisal