Data Source Connection - Unique ID Blank - How do I match.

[PBInonpro]

We have a database we connect to and because it is via gateway, we don't have access to the tables. 

The Unique ID that we build a relationship with on our DIM table is:

UNIQUE_ID

A1

A2

A3

A4

In the database we are connecting to it has:

UniqueID

B1

B2

A2

A3

A4

The problem is when we connect it is the following:

OurDIMTable	GateWayTable
A1
A2	A2
A3	A3
A4	A4

(Not sure if I did that correctly). 

But to fix this I tried using a If statement with 'Blank()', isblank, etc. and nothing seems to work. This small problem is hindering a big report for us. 

Beyond that, I can't verify that it is actually blank (compared to spaces, tab, etc). I downloaded/exported it and it seemed to be blank. Any solutions?