I don't believe this message belongs in the "History" section of AirForums, so hopefully the mods can move it to the proper section.
That said, I assume "null" comes from certain fields the poster may have left blank, such as "city". When the titles/listings auto generate using the information in certain fields, the word "null" is inserted when a blank is encountered. At least that's my guess.
Wally Byam Caravan Club International Historian
Vintage Airstream Club Historian