Minor corrections after review

akka-actor-tests/src/test/scala/akka/serialization/SerializeSpec.scala

@@ -106,7 +106,7 @@ class SerializeSpec extends AkkaSpec(SerializeSpec.serializationConf) {
       }))
       a ! new ObjectOutputStream(new ByteArrayOutputStream())
       expectMsg("pass")
-      a.stop
+      a.stop()
     }
 
     "serialize DeadLetterActorRef" in {

akka-actor/src/main/scala/akka/actor/ActorCell.scala

@@ -112,6 +112,9 @@ trait ActorContext extends ActorRefFactory {
    * @return the provided ActorRef
    */
   def unwatch(subject: ActorRef): ActorRef
+
+  final protected def writeObject(o: ObjectOutputStream): Unit =
+    throw new NotSerializableException("ActorContext is not serializable!")
 }
 
 trait UntypedActorContext extends ActorContext {
@@ -603,7 +606,4 @@ private[akka] final class ActorCell(
       lookupAndSetField(a.getClass, a, "self", self)
     }
   }
-
-  final protected def writeObject(o: ObjectOutputStream): Unit =
-    throw new NotSerializableException("ActorCell/ActorContext is not serializable!")
 }