'/worldborder warning time' or '/worldborder warning distance' without the number param causes an "unknown error"

To reproduce, run either of these commands: /worldborder warning time or /worldborder warning distance.

What I expected: running that command would give help info like all of the other commands.

What actually happened: "An unknown error occurred while attempting to perform this command" is printed to chat. The game log also prints "Couldn't process command: 'worldborder warning time'" for the server thread, but no stacktrace (on neither the integrated nor a dedicated vanilla server).

That causes these 2 strings to go unused as well.