[crumpets]

People use the word NULL and in all caps as well, in particular in bureaucratic processes like those you would encounter at the DMV.

NULL & VOID, etc.

It is entirely reasonable that the system would not accept an empty string for the plate so the process folks worked around that by instructing all employees to write NULL if they couldn't read the plate.

[perl4ever]

Many people who are not programmers per se come into contact with databases that use SQL enough that they might absorb a few random concepts or names for things.

So, some bureaucrat might in fact know "NULL" because they type a command into a database every Tuesday to run a report.