revert accidental patch commit in doc changes

Author: puredanger

src/main/clojure/clojure/core/async.clj

@@ -277,8 +277,6 @@ to catch and handle."
   "returns derefable [val port] if immediate, nil if enqueued"
   [fret ports opts]
   (assert (pos? (count ports)) "alts must have at least one channel operation")
-  (doseq [port ports :when (vector? port)]
-    (assert (not (nil? (nth port 1))) "alts can't put nil on channel"))
   (let [flag (alt-flag)
         ports (vec ports) ;; ensure vector for indexed nth
         n (count ports)

src/test/clojure/clojure/core/async_test.clj

@@ -465,10 +465,3 @@
              :ok
              (catch AssertionError e
                :ko))))))
-
-(deftest test-alts-put-nil-invalid
-  (is
-    (thrown? AssertionError
-      (let [c1 (a/chan)
-            c2 (a/chan)]
-        (a/alts!! [c1 [c2 nil]])))))