using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        List<DateTime? > dates = new List<DateTime? >()

        {new DateTime(2016, 10, 05, 00, 00, 00), null, null, null, new DateTime(2016, 08, 12, 07, 46, 00), null, null};

        DateTime? latest = null;

        for (int i = 0; i < dates.Count; i++)

        {

            if (dates[i].HasValue)

            {

                latest = dates[i];

            }

            else

            {

                dates[i] = latest;

            }

        }

​

        foreach (DateTime item in dates)

        {

            Console.WriteLine(item);

        }

    }

}