using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        string[] accts = new string[] {"234567","134809","34567","124268","0658"};

        string[] results = accts.Where( a => a.Contains("5") ).ToArray();

        DateTimeOffset? begin = null;

        DateTimeOffset start = begin ?? (DateTimeOffset)begin;

        Console.WriteLine(start);

    }

}