(find map key)
Returns the map entry for key, or nil if key not present.
(find {:a 1 :b 2 :c 3} :a)
;;=> [:a 1]
(find {:a 1 :b 2 :c 3} :d)
;;=> nil
user=> (find [:a :b :c :d] 2)
[2 :c]
user=> (find [:a :b :c :d] 5)
nil