输入字符串导致nullreferenceexception的错误是什么?

问题是else情况，我已经在问题行

    static void Main(string[] args)
    {
        XMLData xmldataExample = new XMLData();
        Usergaz usergazExample = new Usergaz();
        UsergazItem usergazitemExample = new UsergazItem();
        UsergazItem item = new UsergazItem();
        string filename = @"C:'Users'565133'Desktop'test.xml";
        Deserialize<XMLData> deserializeobj = new Deserialize<XMLData>();
        Console.WriteLine("Choose 'n1.Serialization'n2.Deserialization'n3.Deserialize only a token");
        //It works when I give tknid input line here
        int inp = Console.Read();
        string tknid = Console.ReadLine();//It doesn't work if I get tknid input here
        if (inp == 1)
        {
            usergazitemExample.getusergazitem();
            usergazExample.getusergaz();
            usergazExample.gazitem.Add(usergazitemExample);
            xmldataExample.getxmldata();
            xmldataExample.gazset.Add(usergazExample);

            serial(xmldataExample, filename);
            Console.WriteLine("Its done");
            Console.ReadKey();
        }
        else if (inp == 2)
        {
            Console.WriteLine("Getting data from xml file");
           // Deserialize<XMLData> deserializeobj = new Deserialize<XMLData>();
            xmldataExample = deserializeobj.deserializefunction(filename);
            List<Usergaz> samplelist = new List<Usergaz>();
            samplelist = xmldataExample.gazset;
            MTable.initialize();
            MTable.usergazzetterset.Add(xmldataExample.updatedtime, samplelist);
            Console.WriteLine("Deserialization complete, check the object");
            Console.ReadKey();
        }

在这个else情况下，我使用tknid进行过滤，但甚至在我从用户输入tknid之前，我得到nullreference异常，说'item'对象是空的。我得到指向控制台的异常。WriteLine行

        else
        {
            //Console.WriteLine("Getting only a specific token Enter the token id");
            //string tknid;
            //tknid = Console.ReadLine(); 
//I intended to give tknid input here, but I cannot do it...
            //Console.WriteLine(tknid);
            //Console.ReadKey();
            //string tknid = "3"; Initializing tknid with this statement works fine


            item = deserializeobj.deserializefunction(filename).gazset[0].gazitem.Where(X => X.id == tknid).FirstOrDefault();
            Console.WriteLine("The value for the token id {0} is {1}", tknid,item.val);
            Console.ReadKey();
        }
    }