#vulnerable code 
                                public void process(Socket socket) {
        SocketInputStream input = null;
        OutputStream output = null;
        try {
            input = new SocketInputStream(socket.getInputStream(), 2048); // 1.读取套接字的输入流
            output = socket.getOutputStream();

            // create HttpRequest object and parse
            request = new HttpRequest(input);
            response = new HttpResponse(output);
            response.setRequest(request);
            response.setHeader("Server", "Mars Servlet Container");
            
            parseRequest(input, output); // 解析请求行，即HTTP请求的第一行内容
            parseHeaders(input); // 解析请求头
            // request.addHeader(name, value); // 将请求头的名/值添加到request对象的HashMap请求头中

            if (request.getUri().startsWith("/servlet/")) {
                ServletProcessor processor = new ServletProcessor();
                //processor.process(request, response);
            } else {
                StaticResourceProcessor processor = new StaticResourceProcessor();
                //processor.process(request, response);
            }

            socket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    } 
                            #location 18 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public void process(Socket socket) {
        SocketInputStream input = null;
        OutputStream output = null;
        try {
            input = new SocketInputStream(socket.getInputStream(), 2048); // 1.读取套接字的输入流
            output = socket.getOutputStream();

            // create HttpRequest object and parse
            request = new HttpRequest(input);
            response = new HttpResponse(output);
            response.setRequest(request);
            response.setHeader("Server", "Mars Servlet Container");
            
            parseRequest(input, output); // 解析请求行，即HTTP请求的第一行内容
            parseHeaders(input); // 解析请求头

            if (request.getRequestURI().startsWith("/servlet/")) {
                ServletProcessor processor = new ServletProcessor();
                //processor.process(request, response);
            } else {
                StaticResourceProcessor processor = new StaticResourceProcessor();
                //processor.process(request, response);
            }

            socket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }