#fixed code
                                public void start() {
        try {
            ChannelFuture future = boot.connect(node.getIp(), node.getSeverPort()).addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(ChannelFuture future) throws Exception {
                    if (future.isSuccess()) {
                        socketChannel = (SocketChannel) future.channel();
                    } else {
                        Log.info("Client connect to host error: " + future.cause() + ", remove node: " + node.getId());
                        getNetworkService().removeNode(node.getId());
                    }
                }
            });
            future.channel().closeFuture().sync();
        } catch (Exception e) {
            //maybe time out or refused or something
            if (socketChannel != null) {
                socketChannel.close();
            }
            Log.error("Client start exception:" + e.getMessage() + ", remove node: " + node.getId());
            getNetworkService().removeNode(node.getId());
        }
    }
#vulnerable code 
                                public void start() {
        try {
            ChannelFuture future = boot.connect(node.getIp(), node.getSeverPort()).sync();
            if (future.isSuccess()) {
                socketChannel = (SocketChannel) future.channel();
            } else {
                System.out.println("---------------client start !success remove node-----------------" + node.getId());
                getNetworkService().removeNode(node.getId());
            }
            future.channel().closeFuture().sync();
        } catch (Exception e) {
            Log.debug("-------------NettyClient start error: " + e.getMessage());
            //maybe time out or refused or something
            if (socketChannel != null) {
                socketChannel.close();
            }
            System.out.println("---------------client start exception remove node-----------------" + node.getId());
            getNetworkService().removeNode(node.getId());
        }
    } 
                            #location 8 
                            #vulnerability type NULL_DEREFERENCE