using System;

using System.Collections.Generic;

using System.Linq;

​

public class user_mstr

{

    public string user_cd;

}

​

public class FakeContext

{

    public List<user_mstr> user_mstr;

}

​

public class Program

{

    private static string strUserCD = "foo";

    private static void FirstUserAsNull()

    {

        try

        {

            Console.WriteLine("OneUserAsNull");

            FakeContext ctx = new FakeContext();

            ctx.user_mstr = new List<user_mstr>() { null, new user_mstr(), new user_mstr() };

            user_mstr vwUser = ctx.user_mstr.FirstOrDefault(x => x.user_cd == strUserCD);

        }

        catch (NullReferenceException e)

        {

            Console.WriteLine(e.Message);

        }

        catch (ArgumentNullException e)

        {

            Console.WriteLine(e.Message);

            Console.WriteLine();

        }

    }

    private static void UserListAsNull()

    {

        try

        {

            Console.WriteLine("UserListAsNull");

            FakeContext ctx = new FakeContext();

            ctx.user_mstr = null;

            user_mstr vwUser = ctx.user_mstr.FirstOrDefault(x => x.user_cd == strUserCD);

        }

        catch (NullReferenceException e)

        {

            Console.WriteLine(e.Message);

        }

        catch (ArgumentNullException e)

        {

            Console.WriteLine(e.Message);

            Console.WriteLine();

        }

    }

​

    private static void CtxAsNull()

    {

        try

        {

            Console.WriteLine("CtxAsNull");

            FakeContext ctx = null;

            user_mstr vwUser = ctx.user_mstr.FirstOrDefault(x => x.user_cd == strUserCD);

        }

        catch (NullReferenceException e)

        {

            Console.WriteLine(e.Message);

            Console.WriteLine();

        }

    }

​

    public static void Main()

    {

        CtxAsNull();

        UserListAsNull();

        FirstUserAsNull();

    }

}