Linq Grop by

using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
  public static void Main()
  {
    var inputDtos = new List<Dto>(){
    new Dto{ fname = "11", lname = "12", age = "13", gender = "1"},
new Dto{ fname = "", lname = "12", age = "13", gender = "1"},
new Dto{ fname = null, lname = "12", age = "13", gender = "1"},
new Dto{ fname = "11", lname = "", age = "13", gender = "1"},
new Dto{ fname = "11", lname = null, age = "13", gender = "1"},
new Dto{ fname = "11", lname = "12", age = "", gender = "1"},
new Dto{ fname = "11", lname = "12", age = null, gender = "1"},
new Dto{ fname = "11", lname = "12", age = "13", gender = ""},
new Dto{ fname = "11", lname = "12", age = "13", gender = null},

new Dto{ fname = "11", lname = "12", age = "13", gender = "1"},
new Dto{ fname = "21", lname = "22", age = "23", gender = "0"},
new Dto{ fname = "21", lname = "22", age = "23", gender = "0"},


};
                     var DuplicateList = (from d in inputDtos
                                         group d by  
                                         new
                                        {
                                            firstName = TrimValueSpace(d.fname),
                                            lastName = TrimValueSpace(d.lname),
                                            birthday = TrimValueSpace(d.age),
                                            gender = TrimValueSpace(d.gender)
                                        }
                        into gr
                                         where gr.Count() > 1
                                               && !string.IsNullOrWhiteSpace(gr.Key.firstName)
                                               && !string.IsNullOrWhiteSpace(gr.Key.lastName)
                                               && !string.IsNullOrWhiteSpace(gr.Key.birthday)
                                               && !string.IsNullOrWhiteSpace(gr.Key.gender)
                                         select gr.Key).ToList();

if (DuplicateList != null )
                        {
          Console.WriteLine("ok  --- " + DuplicateList.Count);

                        }
                        var sfdfd = "222";

          Console.WriteLine(sfdfd ?? "0");


  }

        private static string TrimValueSpace(string value)
        {
            if (string.IsNullOrWhiteSpace(value))
            {
                return string.Empty;
            }
            else
            {
                return value.Replace(" ", string.Empty).Replace("　", string.Empty);
            }
        }
  
}
public class Dto{
    public string fname {get; set;}
    public string lname {get; set;}
    public string age{get; set;}
    public string gender{get; set;}
  }