Inserting at top can throw an exception.
(require '[clojure.zip :as z])
(-> (z/vector-zip [])
(z/insert-right :foo)
z/root)
;; Execution error: Insert at top
However, making any edit will cause inserts to be silently ignored.
(-> (z/vector-zip [])
(z/replace [])
(z/insert-right :foo)
z/root)
;; []
Not a big deal, but I missed a bug that would have been otherwise caught.
