Index: lams_tool_scratchie/src/java/org/lamsfoundation/lams/tool/scratchie/web/action/LearningWebsocketServer.java
===================================================================
diff -u -r63ff5aaa19e3fb53810266ade4fc2e9433c09d44 -r7ad5836f13935fb4a998edb7e6579e5d0a015e3d
--- lams_tool_scratchie/src/java/org/lamsfoundation/lams/tool/scratchie/web/action/LearningWebsocketServer.java	(.../LearningWebsocketServer.java)	(revision 63ff5aaa19e3fb53810266ade4fc2e9433c09d44)
+++ lams_tool_scratchie/src/java/org/lamsfoundation/lams/tool/scratchie/web/action/LearningWebsocketServer.java	(.../LearningWebsocketServer.java)	(revision 7ad5836f13935fb4a998edb7e6579e5d0a015e3d)
@@ -217,8 +217,12 @@
 	responseJSON.put("close", true);
 	String response = responseJSON.toString();
 
+	Set<Session> sessionWebsockets = LearningWebsocketServer.websockets.get(toolSessionId);
+	if (sessionWebsockets == null) {
+	    return;
+	}
 	// make a copy of the websocket collection so it does not get blocked while sending messages
-	Set<Session> sessionWebsockets = new HashSet<Session>(LearningWebsocketServer.websockets.get(toolSessionId));
+	sessionWebsockets = new HashSet<Session>(sessionWebsockets);
 	for (Session websocket : sessionWebsockets) {
 	    websocket.getBasicRemote().sendText(response);
 	}