Bug with adding and removing `nil`

[DrSplinter]

There is a problem with the following:

(require '[data.deque :as dq])
(assert (= (list 2 nil)
           (-> (dq/deque)
               (dq/add-first nil)
               (dq/add-first nil)
               (dq/add-first 2)
               dq/remove-last
               seq)))

Interesting is the fact that if we add-last and then remove-first it works correctly.

[namenu]

When removing an element, the finger tree may shrink by checking returning nil.
It seems nils in the example is causing the wrong behavior.
(In general, inserting nil into a collection is not recommended.)

I'll make a PR not to use nil as a marker.
Thanks.

[DrSplinter]

Oh, OK then. I'll use some keyword like :clojure.spec.alpha/invalid keyword used in spec :-)

Thank you too

(should I close this Issue?)

[namenu]

No, it's an obvious bug of data.deque so let's keep this open. 😃