merge-nilable.clj

(s/def ::m1 (s/keys :req [::a ::b]))
(s/def ::a int?)
(s/def ::b int?)
(s/def ::x int?)
(s/def ::y int?)
(s/def ::ab (s/keys :req [::a ::b]))
(s/def ::xy (s/keys :req [::x ::y]))
(s/def ::m (s/merge ::ab (s/nilable ::xy)))
(s/exercise ::m)

(set (map (comp vec keys first) (s/exercise ::m)))
;; actual => #{[:user/a :user/b :user/x :user/y]}
;; expected => #{[:user/a :user/b]
;;               [:user/a :user/b :user/x :user/y]}