Apparently some guy in California thought it would be cute to get “NULL” as his license plate. He apparently hoped it would cause his plate to get ignored in the system (which seems unlikely). However instead he started getting tickets for other cars that didn’t have a plate entry recorded (i.e. were NULL in the DB). While the bad charges were removed, they didn’t actually fix their software, they just told him to change his plate (he didn’t), so he continues to get new fines.