Assuming that records with a "blank" value for this particular field are intended to indicate the abscense of information (ie: null) then you should do your part to try and fix the data, and ensure that the integrity of the system.

If you're designing a new schema, and you tell a developer that they should assume any "blank" string field should be treated the same as null, is like telling a developer that this varchar(2) column is a "boolean", and "if the value looks like the word 'no' (or 'N' or ' N' or 'n ', etc...) then it's 'false', otherwise consider it 'true'."

However...

It sounds like you are talking about an existing system, with a lot of existing data, and a lot of existing code that uses that data ... in which case, any new code should try to "play by the rules" -- whatever those rules are.

I don't really blame this guy for not being happy with your answer, and escalating the issue ... but I hope he did that in addition to making his code more robust, and liberal in what it accepts.

If he just complained to get out of changing his own code, then he sounds like a real Ass.