Commented out the message class serialization and left

a comment as to why: in 3.1 there is a default service
that automatically does this on clients.

jme3-examples/src/main/java/jme3test/network/TestChatClient.java

@@ -114,7 +114,12 @@ public static String getString(Component owner, String title, String message, St
     }
 
     public static void main(String... args) throws Exception {
-        TestChatServer.initializeClasses();
+
+        // Note: in JME 3.1 this is generally unnecessary as the server will
+        // send a message with all server-registered classes.
+        // TestChatServer.initializeClasses();
+        // Leaving the call commented out to be illustrative regarding the
+        // common old pattern.
 
         // Grab a host string from the user
         String s = getString(null, "Host Info", "Enter chat host:", "localhost");