A shell colon does nothing. Use it anyway

“the point is to show that the null-command can be used in places where a command is required, but nothing is desired.”

The colon has been in shells since 1971 and most people have never typed one on purpose. Pair it with ${VAR:?message} and you get argument validation in one line, no if block. Fifty-five years of accumulated shell trivia exists because nobody ever gets to delete anything.