Odd exception on lazy sequence

[KJO]

I'm stumped on this. I have a function that returns a lazy sequence (let's call
it lzs - it's produced by another function, and for this exercise I def'd it

in the REPL from `*1'). It's a sequence of maps.

When I apply a merge-with operation to the lazy sequence. I get the following
error.

  class clojure.lang.PersistentHashSet cannot be cast to class 
  java.lang.Comparable (clojure.lang.PersistentHashSet is in unnamed 
  module of loader 'app'; java.lang.Comparable is in module java.base 
  of loader 'bootstrap'

If I apply the same operation on a `doall' of the sequence, I also get the error.

However, if I fully realize the sequence in the REPL and feed it into the
merge operation, I don't get the error. There's really no magic in the merge-with
operation, it just conj's some sets.

Any ideas?

The relevant code is below:
;; FAILS
(apply
  merge-with
  px-tran-netter-ex
  lzs)

;; FAILS
(apply
  merge-with
  px-tran-netter-ex
  (doall lzs))

;; NO PROBLEM HERE with lzs realized and fed back in
(apply
  merge-with
  px-tran-netter-ex
  '({:fund {:src-ax-id #{nil :ax-m01}}}
    {:fund {:src-ax-id #{:ax-m01}}}
    {:fund {:src-ax-id nil}}
    {:fund {:src-ax-id :ax-m01}}
    {:fund {:src-ax-id #{:ax-m01}}}
    {:fund {:src-ax-id #{nil :ax-m01}}}
    {:fund {:src-ax-id #{:ax-m01}}}
    {:fund {:src-ax-id nil}}
    {:fund {:src-ax-id :ax-m01}}
    {:fund {:src-ax-id #{:ax-m01}}}))

The px-tran-netter-ex is 

(defn px-tran-netter-ex
  [ov nv]
  (if (nil? ov)
    nv
    (update
      ov
      :src-ax-id
      (fn px-tran-set-merger
        [lv rv]
        (if (some? rv)
          (conj
            (if (set? lv)
              lv
              (if (some? lv)
                #{lv}
                #{}))
            rv)
          lv))
      (:src-ax-id nv)))) 

[KJO]

OK. I got some super guidance from p-himik on the Slack channel (Thank you!).

Essentially there was a TreeSet in one of the sets to be conj'ed and that was causing the exception. Apparently, it's not a trivial matter to conj tree-sets :-).