Make disj nil-aware

Refers #360

Signed-off-by: Stuart Halloway <stu@thinkrelevance.com>

Author: kotarak

src/clj/clojure/core.clj

@@ -1168,12 +1168,14 @@
   {:added "1.0"}
   ([set] set)
   ([^clojure.lang.IPersistentSet set key]
-   (. set (disjoin key)))
+   (when set
+     (. set (disjoin key))))
   ([set key & ks]
-   (let [ret (disj set key)]
-     (if ks
-       (recur ret (first ks) (next ks))
-       ret))))
+   (when set
+     (let [ret (disj set key)]
+       (if ks
+         (recur ret (first ks) (next ks))
+         ret)))))
 
 (defn find
   "Returns the map entry for key, or nil if key not present."

test/clojure/test_clojure/data_structures.clj

@@ -728,6 +728,7 @@
 
   ; identity
   (are [x] (= (disj x) x)
+      nil
       #{}
       #{1 2 3}
       ; different data types
@@ -753,6 +754,9 @@
       (sorted-set 1 2) )
 
   (are [x y] (= x y)
+      (disj nil :a) nil
+      (disj nil :a :b) nil
+
       (disj #{} :a) #{}
       (disj #{} :a :b) #{}