#fixed code
                                @Override
    protected void channelRead0(ChannelHandlerContext ctx, GetTokenMessage message) throws Exception {
        String dashBoardIdString = message.body;

        Long dashBoardId;
        try {
            dashBoardId = Long.parseLong(dashBoardIdString);
        } catch (NumberFormatException ex) {
            throw new InvalidCommandFormatException(String.format("Dash board id %s not valid.", dashBoardIdString), message.id);
        }

        User user = Session.findUserByChannel(ctx.channel(), message.id);
        String token = userRegistry.getToken(user, dashBoardId);

        ctx.writeAndFlush(produce(message.id, message.command, token));
    }
#vulnerable code 
                                @Override
    protected void channelRead0(ChannelHandlerContext ctx, GetTokenMessage message) throws Exception {
        String dashBoardIdString = message.body;

        Long dashBoardId;
        try {
            dashBoardId = Long.parseLong(dashBoardIdString);
        } catch (NumberFormatException ex) {
            log.error("Dash board id {} not valid.", dashBoardIdString);
            ctx.writeAndFlush(produce(message.id, INVALID_COMMAND_FORMAT));
            return;
        }

        User user = Session.findUserByChannel(ctx.channel());
        String token = userRegistry.getToken(user, dashBoardId);

        ctx.writeAndFlush(produce(message.id, message.command, token));
    } 
                            #location 15 
                            #vulnerability type NULL_DEREFERENCE