In the late 80's I taught an Introduction to Data Processing class (CDP-101) at a Junior College.  On one of the scheduled tests which covered basic flow charting, I presented a flow chart to the students.

There were three questions each giving values for input, and asking what would be printed out from the program displayed by the flow chart.  The best answer to the second set of values was to leave the answer blank.  Nothing was also acceptable.

However, most put zero in the block and got it wrong.

I was trying to teach the difference between zero, null, and nothing.  While there were several screams of pain, they got the lesson.  It now appears that I too have been taught a lesson, one I obviously needed to learn.

Please note, that the set of laws (orginally presented to us)  has been removed from my Book of Shadows and replaced with the words

"Always Question" in a very large font.

Humbly yours,
White Pine