The Null value in spreadsheets; parity with CSV

I've been thinking a lot about RSV. I just rewatched your video about importing/exporting with LibreOffice Calc, and I wondered if that spreadsheet can represent RSV's Null value. What did you do about nulls when you wrote the extension?

I've briefly looked in Excel's documentation and don't see any mention of a null value.

To try and supplant CSV, I think RSV's Null value might be a hangup.