#vulnerable code 
                                String assignToken(User user, int dashId, int deviceId, String newToken) {
        // Clean old token from cache if exists.
        DashBoard dash = user.profile.getDashByIdOrThrow(dashId);
        Device device = dash.getDeviceById(deviceId);

        String oldToken = deleteDeviceToken(device);

        //assign new token
        device.token = newToken;
        cache.put(newToken, new TokenValue(user, dash, device));

        user.lastModifiedTs = System.currentTimeMillis();

        log.debug("Generated token for user {}, dashId {}, deviceId {} is {}.", user.email, dashId, deviceId, newToken);

        return oldToken;
    } 
                            #location 9 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                RegularTokenManager(Iterable<User> users) {
        this.cache = new ConcurrentHashMap<String, TokenValue>() {{
            for (User user : users) {
                if (user.profile != null) {
                    for (DashBoard dashBoard : user.profile.dashBoards) {
                        for (Device device : dashBoard.devices) {
                            if (device.token != null) {
                                put(device.token, new TokenValue(user, dashBoard, device));
                            }
                        }
                    }
                }
            }
        }};
    }