Optimize the Linq Query adding null just for filtering

Pasting the working version of code, try it on visual studio or Linqpad, Main question post code in the end

void Main()
{
    PGSSnapshotDataContract pgs = new PGSSnapshotDataContract();
    ProductMovementActivityOutputData ob1 = new ProductMovementActivityOutputData(new DateTime(2016, 08, 10, 06, 57, 20), DateTime.Now, "17M00816A", "1155581", "InProgress");
    ProductMovementActivityOutputData ob3 = new ProductMovementActivityOutputData(DateTime.Now, DateTime.Now, "17M00805B", "1158479", "InProgress");
    ProductMovementActivityOutputData ob2 = new ProductMovementActivityOutputData(new DateTime(2016, 08, 10, 04, 40, 50), new DateTime(2016, 08, 10, 09, 57, 20), "M2", "1155581", "InProgress");
    ProductMovementActivityOutputData ob4 = new ProductMovementActivityOutputData(new DateTime(2016, 08, 10, 07, 00, 00), new DateTime(2016, 08, 10, 09, 00, 00), "M2", "1158479", "InProgress");
    ProductMovementActivityOutputData ob5 = new ProductMovementActivityOutputData(new DateTime(2016, 08, 10, 09, 10, 00), new DateTime(2016, 08, 10, 09, 20, 00), "M2", "1158479", "InProgress");
    ProductMovementActivityOutputData ob6 = new ProductMovementActivityOutputData(new DateTime(2016, 08, 11, 07, 00, 00), new DateTime(2016, 08, 11, 09, 00, 00), "M2", "1158479", "InProgress");
    pgs.ProductMovements.Add(ob1);
    pgs.ProductMovements.Add(ob2);
    pgs.ProductMovements.Add(ob3);
    pgs.ProductMovements.Add(ob4);
    pgs.ProductMovements.Add(ob5);
    pgs.ProductMovements.Add(ob6);

    var productMovementsList = pgs.ProductMovements.OrderBy(b => b.StartTime).GroupBy(x => x.SourceCode) ;


//  foreach (var v in productMovementsList)
//      Console.WriteLine(v);

    var list = productMovementsList.SelectMany(x => x.Zip(x.Skip(1), (a, b) => (a.EndTime > b.StartTime) ? a.SourceCode : null).Where(y => y != null));

    foreach (var l in list)
        Console.WriteLine(l);
}

public class ProductMovementActivityOutputData
{
    public ProductMovementActivityOutputData(DateTime start, DateTime end, String src, String dest, String stat)
    {
        StartTime = start;
        EndTime = end;
        SourceCode = src;
        DestinationCode = dest;
        Status = stat;
    }
    public DateTime StartTime { get; set; }
    public DateTime EndTime { get; set; }
    public string SourceCode { get; set; }
    public string DestinationCode { get; set; }
    public string Status { get; set; }
}

public class PGSSnapshotDataContract
{
    public PGSSnapshotDataContract()
    {
        this.ProductMovements = new List<ProductMovementActivityOutputData>();
    }
    public List<ProductMovementActivityOutputData> ProductMovements { get; set; }
}

Question:

Want to optimize this piece of code in the Main function:

var list = productMovementsList.SelectMany(x => x.Zip(x.Skip(1), (a, b) => 
          (a.EndTime > b.StartTime) ? a.SourceCode : null).Where(y => y != null));

Here first I deliberately add value SourceCode or null, which is just to be filtered out in the end using Where, is there a better mechanism