DLookup and Nz

[Xandru]

I have two tables- One Tbl_Course and the other Tbl_Grading.
I created a query from Tbl_Course and I add an expression and I named it Gradings to look from Tbl_Grading for grades.

I wrote this Statement

Gradings: DLookUp("Grading","Tbl_Grading","Mark=" &[Mark])
it works perfectly, but the empty fields comes with a #Error.

I would like to add Nz, so when the field is empty it shows "Waiting For Result"

Any Help please!