Null value in function (1 Viewer)

Hi,

I am trying to using an iff statement to pick up null values, but I don't know what to type in the function. I tried using "is null", but got an invalid message.

Does anyone know what value I should type in to get null value in the function below?

IIf([popi_r2a] is null","",[popi_r2a])


Thanks.

Use the following.

NZ([popi_r2a],'')