The NULL_BUCKET also has its own section of emitted moxi statistics. If you see a NULL_BUCKET in your "stats proxy" output, it's because you're talking to a moxi that's been started (via command-line arguments) as a "gateway moxi". In this situation, when a client first connects, it is assigned to this "/dev/null" bucket. The client then can do a SASL authentication to be associated with a non-null bucket.