Welcome! Please see the About page for a little more info on how this works.
A full example is here: removing the primitive hint on line 29 will resolve the error, or making the call on line 49 be a number directly will also work.
Some discussion is available here: https://clojurians.slack.com/archives/C03S1KBA2/p1596323055271400
You get a similar success result if you return a number instead of nil in the :survey case. Curious.
Logged with a simpler repro at https://clojure.atlassian.net/browse/CLJ-2580