multi-key-stable-sort-with-nils

(defn sort-records
  "Stable multi-key sort; specs are [:age :asc]. nil compares lower than any other value."
  [rows & specs]
  (sort (fn [a b]
          (or (some (fn [[k dir]]
                      (let [c (compare (get a k) (get b k))]
                        (when-not (zero? c)
                          (if (= :desc dir) (- c) c))))
                    specs)
              0))
        rows))

;; (sort-records [{:age 2} {:age nil}] [:age :asc])