The help file is very unclear about that, imo it's not really implying you can use 0 either when executing a command or when evaluating a line.
I agree though, it should be possible not to use a value (or a value representing 'none of the above'), at least when executing a command, because there are difference when a command is executed from the editbox or not.
You can use this forum to report a problem with the docs.
