AutoCAD Inventor :: How To Filter A Selectset

I need to filter a selectset, in order to have only the objects I need (here balloons) in a collection.

I tried to test using "Typeof", the problem is some objects in the selectset are "empty".

What are thes "empty" objects ? And, more important, how can I found them ?

My current code is :

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Dim oSelection As SelectSet

Dim oSelectedBalloons As New Collection

Dim selectedObj As Object

[Code]...

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This function if objects in the selectset are not empty.

How can I adapt it for empty objects ? Something like "if selectedObj = Nothing..."