Index allowing duplicates on Access table

[klnlsu]

CustItemTableSpecs.pdf

The attachment contains documentation for my customer item cross-reference table in my database. Please note the MasterKey index. I want Access to NOT allow a duplication on the combination of these three fields. The problem is that the CustAltAddr field can be NULL in my data. The table is allowing me to enter duplicates when this field is NULL and the other two fields are equal. If I enter an empty string ("") in this field and the other two fields are equal, Access doesn't allow it. I can alter my database coding to replace NULLs with ""s, but that will be very tedious! I have tried setting the "Ignore Nulls" value in my index to Yes and then No and neither setting has any affect. Can someone help? (I have never liked the way Access handles NULLs)

[June7]

Just might need to use VBA to do validation.