CLJ-2580 correct case expr branch analysis

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

Author: ghadishayban

src/jvm/clojure/lang/Compiler.java

@@ -1375,6 +1375,8 @@ static Class maybeJavaClass(Collection<Expr> exprs){
         if (!e.hasJavaClass())
             return null;
         Class c = e.getJavaClass();
+        if (c == null)
+            return null;
         if (match == null)
             match = c;
         else if (match != c)

test/clojure/test_clojure/compilation.clj

@@ -438,3 +438,8 @@
     (is (= 42 (compilation.JDK8InterfaceMethods/staticMethod0 42)))
     (is (= "test" (compilation.JDK8InterfaceMethods/staticMethod1 "test")))
     (is (= 1 (if (compilation.JDK8InterfaceMethods/staticMethod2 true) 1 2)))))
+
+(deftest CLJ-2580
+  (testing "CLJ-2580 Correctly calculate exit branches of case"
+    (is (zero? (let [d (case nil :x nil 0)] d)))
+    (is (nil? (let [d (case nil :x 0 nil)] d)))))