ASP.NET Linq排序

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            List<fpk> list = new List<fpk>()
            {
                new fpk {  fpkid=1004,createtime=Convert.ToDateTime("2020-11-20 12:19:48") },
                new fpk {  fpkid=1003,createtime=Convert.ToDateTime("2020-11-20 15:19:47") },
                new fpk {  fpkid=1001,createtime=null },
                new fpk {  fpkid=1002,createtime=null }
            };

            
            var result = (from st in list orderby st.createtime ascending, st.fpkid ascending select st).FirstOrDefault();
            Console.WriteLine(result.fpkid);

            Console.ReadKey();

        }
    }

    public class fpk
    {
        public int fpkid { get; set; }
        public DateTime? createtime { get; set; }
    }
}