I think you should copy your db, compact/repair the copy, zip it and post here. What I wrote works in the immediate window where my data is null or contains a ? character. I suspect Davegri's version worked as well. We've passed 19 posts now for what should be a fairly simple problem. Since this is just a learning exercise (as you mentioned) there won't be sensitive data to worry about?
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.