error: Specified cast is not valid.

Question

Hello everyone,

 

After implement this code, 

 

public class MainUserLogin
   {
       public Nullable<DateTime> LogInTime { get; set; }
       public Nullable<DateTime> LogOutTime { get; set; }
       public Int64 Id { get; set; }
       public string FirstName { get; set; }
       public string SurName { get; set; }
   }

List< MainUserLogin> objUserSetUp = userList.Select(m => new  MainUserLogin()
               {
                   Id = m.Field<Int64>("Id"),
                   FirstName = m.Field<string>("FirstName"),
                   SurName = m.Field<string>("SurName"),
                   LogInTime = m.Field<DateTime?>("LogInTime"),
                   LogOutTime = m.Field<DateTime?>("LogOutTime")
               }).ToList();

If LoginTime or LogOutTime is existing null then the error is happening "Specified cast is not valid."

How can I solve this error?