Index: lams_learning/src/java/org/lamsfoundation/lams/learning/command/CommandWebsocketServer.java
===================================================================
RCS file: /usr/local/cvsroot/lams_learning/src/java/org/lamsfoundation/lams/learning/command/Attic/CommandWebsocketServer.java,v
diff -u -r1.1.2.2 -r1.1.2.3
--- lams_learning/src/java/org/lamsfoundation/lams/learning/command/CommandWebsocketServer.java	11 Aug 2016 13:19:27 -0000	1.1.2.2
+++ lams_learning/src/java/org/lamsfoundation/lams/learning/command/CommandWebsocketServer.java	28 Dec 2016 10:33:40 -0000	1.1.2.3
@@ -149,9 +149,17 @@
      */
     @OnClose
     public void unregisterUser(Session session, CloseReason reason) {
+	String login = session.getUserPrincipal().getName();
+	if (login == null) {
+	    return;
+	}
+
 	Long lessonId = Long.valueOf(session.getRequestParameterMap().get(AttributeNames.PARAM_LESSON_ID).get(0));
 	Map<String, Session> lessonWebsockets = CommandWebsocketServer.websockets.get(lessonId);
-	String login = session.getUserPrincipal().getName();
+	if (lessonWebsockets == null) {
+	    return;
+	}
+
 	lessonWebsockets.remove(login);
     }