Remove empty subvalues

ensure.clj

(let [ensure* (stay-then-continue (if-path empty? (terminal-val NONE)))]
  (defdynamicnav ensure [& path]
    (interleave (repeat (count path) ensure*) path)
    ))

(setval [:a (ensure :b :c)] NONE {:a {:b {:c 1}}})
;; => {}

(setval [:a (ensure :b :c)] NONE {:a {:b {:c 1} :d 2}})
;; => {:a {:d 2}}

(setval [ALL (ensure :a ALL :b)]
  NONE
  [{:a [{:b 3}]}
   {:a [{:b 2 :c 1}]}])
;; => [{:a [{:c 1}]}]