Error Prone: Enable and fix GetClassOnEnum

Change-Id: I42b0df3926b8c8633067e5d8cab81987fb6a71bf
diff --git a/tools/BUILD b/tools/BUILD
index c3cc95b..8d34156 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -60,7 +60,7 @@
         "-Xep:FragmentNotInstantiable:ERROR",
         "-Xep:FunctionalInterfaceClash:ERROR",
         "-Xep:FutureReturnValueIgnored:ERROR",
-        #"-Xep:GetClassOnEnum:ERROR",
+        "-Xep:GetClassOnEnum:ERROR",
         "-Xep:ImmutableAnnotationChecker:ERROR",
         #"-Xep:ImmutableEnumChecker:ERROR",
         "-Xep:IncompatibleModifiers:ERROR",