Fix NotFoundExeptions for setSession event in Socket.IO implementation

src/main/java/de/thm/arsnova/services/SessionService.java

@@ -65,7 +65,12 @@ public class SessionService implements ISessionService {
 	public final Session joinSession(final String keyword, final UUID socketId) {
 		/* Socket.IO solution */
 
-		Session session = databaseDao.getSession(keyword);
+		Session session = null;
+		try {
+			session = databaseDao.getSession(keyword);
+		} catch (NotFoundException e) {
+
+		}
 		if (null == session) {
 			userService.removeUserFromSessionBySocketId(socketId);
 

src/main/java/de/thm/arsnova/socket/ARSnovaSocketIOServer.java

@@ -112,11 +112,12 @@ public class ARSnovaSocketIOServer {
 		server.addEventListener("setSession", Session.class, new DataListener<Session>() {
 			@Override
 			public void onData(SocketIOClient client, Session session, AckRequest ackSender) {
-				sessionService.joinSession(session.getKeyword(), client.getSessionId());
-				/* active user count has to be sent to the client since the broadcast is
-				 * not always sent as long as the polling solution is active simultaneously */
-				reportActiveUserCountForSession(session.getKeyword());
-				reportSessionDataToClient(session.getKeyword(), client);
+				if (null != sessionService.joinSession(session.getKeyword(), client.getSessionId())) {
+					/* active user count has to be sent to the client since the broadcast is
+					 * not always sent as long as the polling solution is active simultaneously */
+					reportActiveUserCountForSession(session.getKeyword());
+					reportSessionDataToClient(session.getKeyword(), client);
+				}
 			}
 		});