Ho do I check null value in a column of a ComboBox?

Hi
I have code that works well when Me.Kombinationsruta145.Column(8) contains a value.
But if the value in column (8) is Null, my If clause doesnt trap it.
The second part of the "If", after Else is always performed.

How can I stop the code and give the user a message when Me.Kombinationsruta145.Column(8) has a Null value?

I receive this error in line 190
Error 13 (Type mismatch) in procedure Kombinationsruta145_AfterUpdate,line 190

          Dim RecipeInChoosen As Long
          Dim RecipeInTank As Long

140       If (IsNull(Me.Kombinationsruta145.Column(8))) Then
              'Debug.Print Me.Kombinationsruta145.Column(8) & "column 8"
150           DoCmd.OpenForm "WarningOrNoteGeneric"
160           Forms!WarningOrNoteGeneric.TheMessage = "There is no recipe linked to this product in Article Index. Please close Filling Records and update Article index."
170           Exit Sub
180       Else
190           RecipeInChoosen = Me.Kombinationsruta145.Column(8)
200           RecipeInTank = Forms![bryggning tappning från lagertank]![Tappning Ingående batcher i en överföring underformulär].Form![recept]
              'Debug.Print RecipeInChoosen & "In choosen"
              'Debug.Print RecipeInTank & "In Tank"
210       End If

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Best
Peter