California security researcher Droogie came up with what seemed like a good way to avoid having to pay any parking tickets issued to his vehicle: He ordered a vanity license plate emblazoned with "NULL," expecting that (like in this xkcd comic) when the ticket was entered into the the DMV database, it would consider the "NULL" entry to be "the special marker used in Structured Query Language to indicate that a data value does not exist in the database." But that's not quite the way things went. From Ars Technica:
First, Droogie got a parking ticket, incurred for an actual parking infraction—so much for being invisible. Then, once a particular database of outstanding tickets had associated the license plate NULL with his address, it sent him every other ticket that lacked a real plate. The total came to $12,049 worth of tickets. Droogie told the DEF CON audience that he received little sympathy from either the California DMV or the Los Angeles Police Department, both telling him to just change his plate to something else. That remains something he refuses to do.
Although the initial $12,000-worth of fines were removed, the private company that administers the database didn't fix the issue and new NULL tickets are still showing up.