It looks like one problem is from the first line in that alias...
if ($prop == noop) { return $($+(%,wait:,$cid,:,$1),2) }
You are evaluating that variable... that doesn't make any sense if you're using that in a /set command. First, a /set needs a % before it, which this would never have, and second, if this variable doesn't already have data, then it will be $null.
The result of this is that anywhere there is a $nwait().noop, it will be replaced with $null or a value (not a variable).
However, that should still leave you with...
/set $null %wait:$cid:$chan $nick
(where the $cid and $chan are evaluated)
And that should not throw that error even with the $null. So that line isn't going to affect anything even though it's not valid the way it's used. From testing just the /set command with the nWait alias, it doesn't give me an error, which is what I'd expect with that being $null. Now, if both $nwait()'s had .noop, then the error would be expected. I'm not sure why you'd be having the error.
