What is `item_type` 4?

[ReagentX]

There is an int column in the messages table called item_type. Normal messages are 0, channel announcements that update the room name are 2. I have a third item_type in my database, "aptly" named 4, and it seems to be a fully null message (no text or blob data, no associated message, nothing). What does 4 represent? Is there a 1?