POMBA: Validation service should not throw violation errors when a builder returns null

When looking at data comparisons between AAI / SDNC, I saw a couple of violations on the board where the attribute exists in AAI, but it does not in SDNC. 

Here, the value returned is NULL.  Since the NULL does not match a value from AAI, we throw a violation

If a value is not supposed to exist or is not returned, this should be ignored during the comparison