(lists/mapcat (fn [x] [.x .x]) [a b])
(lists/mapcat (fn [x] [.x]) [])
(lists/mapcat (fn [x] (if (= .x 0) [] [.x])) [0 1 0 2])
(lists/mapcat (fn [x] [.x]) null)
(lists/mapcat (fn [x] null) [a b])
(lists/mapcat (fn [a b] [.a .b]) [1 2] [a])
(lists/mapcat (fn [a b c] [.a .b .c]) [1 2] [a b] [false null])
(lists/mapcat :fn/identity [[[a]] [[b]]])
(lists/mapcat :fn/identity [[null false] [] [0]])