Retrieve Nulls in an Access query

I have a query pulling information from a table of 800 records.  The query has a field that is linked to a combo box with the default value of "*".  The query, when using "*", will only pull back values that are in the field.  It will not pull back Nulls in the field.  I want everything to come back when ising "*".  I tried wrapping my criteria in Nz() but that doesn't work.  It still only pulls back values that exist.  I current have this now:

Like Nz([Forms]![frm_Campus_offer_Main]![CboFunction]) & "*"

Is there a way to write the criteria to pull back everything when the combo box is "*", including nulls?
marku24Asked:
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als315Commented:
I prefer to build separate column:
IIF(isnull([Forms]![frm_Campus_offer_Main]![CboFunction]),True,IIF([YourField] like ([Forms]![frm_Campus_offer_Main]![CboFunction] & "*"),true, false))
with criteria: True
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