Forms :: Advanced Search (MultiField) - Add Combobox?

I created Advanced search (Multi- Field) form and its work perfect but I want to add a combo box for search [Date Removed] and the options is "Active" and "Inactive".

my table include:
[Location]
[Date Installed]
[Installed by]
[EquipmentTag]
[Date Removed]
...

The users may not enter [Date Removed] which mean its Null ( also which mean in my project company / Combo box its "Active" ).

In another hand, if users enter [Date Removed] which mean it's not Null ( also which mean in my project company / Combo box its "Inactive").

In short, if user chose "Active" it will search for nulls/empty column in [Date Removed]
if user chose "Inactive" it will search for filled column in [Date Removed]

The code is attached:-

Private Function BuildFilter() As Variant
Dim varWhere As Variant
Dim tmp As String
tmp = """"
Const conJetDate = "#mm/dd/yyyy#"

[Code] .....