'Else' is not required in 'when' if Unit is expected

compiler/testData/codegen/box/when/noElseAssigned.kt

@@ -0,0 +1,9 @@
+fun box(): String {
+    var r = "Fail 0"
+    val x = 1
+    val y: Unit = when (x) {
+        1 -> { r = "OK" }
+        2 -> { r = "Fail 1" }
+    }
+    return r
+}