Revit addin code to find and remove elevation marker tags that have no views associated to it

Revit Remove Empty Elevation Marker Tags

[Transaction(TransactionMode.Manual)]
 public class CmdMain : IExternalCommand
 {

   /// <summary>
   /// Command
   /// </summary>
   /// <param name="commandData"></param>
   /// <param name="message"></param>
   /// <param name="elements"></param>
   /// <returns></returns>
   public Result Execute(ExternalCommandData commandData, ref string message, ElementSet elements)
   {
     try
     {

       Document m_doc = commandData.Application.ActiveUIDocument.Document;
       int m_cnt = 0;

       IEnumerable<ElevationMarker> m_elem = from e in new FilteredElementCollector(m_doc)
                                  .WhereElementIsNotElementType().OfClass(typeof (ElevationMarker))
                                  let em = e as ElevationMarker
                                  where em.HasElevations() == false
                                  select em;

       using (Transaction t = new Transaction(m_doc))
       {
         if (t.Start("Delete Empty Elevation Marker Tags") == TransactionStatus.Started)
         {
           foreach (var x in m_elem.ToList())
           {
             m_doc.Delete(x.Id);
             m_cnt++;
           }
           t.Commit();
         }
       }

       // Results
       clsUtility.ShowTaskDialog(
         "Results", 
         "Deleted Elevation Markers", 
         string.Format("Removed {0} Empty Elevation Marker Tags", m_cnt));

       return Result.Succeeded;
     }
     catch (Exception ex)
     {
       clsUtility.ShowTaskDialog(
         "Failure",
         "Deleting Elevation Markers",
         string.Format("Failed: \n{0}", ex));
       return Result.Cancelled;
     }
   }

 }

   /// <summary>
   /// Quick basic task dialog
   /// </summary>
   /// <param name="titleText"></param>
   /// <param name="largeText"></param>
   /// <param name="smallText"></param>
   internal static void ShowTaskDialog(string titleText, string largeText, string smallText)
   {
     using (TaskDialog td = new TaskDialog(titleText))
     {
       td.CommonButtons = TaskDialogCommonButtons.Ok;
       td.DefaultButton = TaskDialogResult.Ok;
       td.TitleAutoPrefix = false;
       td.MainInstruction = largeText;
       td.MainContent = smallText;
       td.Show();
     }
   }