System.NullReferenceException was unhandled by user code
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=MeasurePointsExport
  StackTrace:
       at MeasurePointsExport.MainForm.<butExport_Click>d__4.MoveNext() in G:\!!!Новые проекты C#\github\lers-uchet\MeasurePointsExport\MeasurePointsExport\MainForm.cs:line 233
  InnerException: