I know, but none of the others 'variables' which can only be accessed in events are behaving this way.
I mostly reported it because I can't think of any other identifier doing that, so it feels inconsistent ($hotlink could be returning $null without halting, like the others).
But that being said, I remember you saying you wished you made some features more 'strict', and I agree, so I guess this is nice.
One thing: could the error message be changed to be explicit regarding how $hotlink can only be used from on hotlink? Maybe like how $input reports "$input: cannot use in event" for critical events, I think the current error is not so clear.