Closed Unassigned: Object reference not set to an instance of an object [8960]

__Resolved in Patch #[14484](https://www.codeplex.com/Download?ProjectName=closedxml&DownloadId=679794). Pending merge into latest__

Hi again,

Seems I've run into an issue with opening Excel documents generated by Microsoft's OpenXML. I receive an "Object reference not set to an instance of an object" error when trying to open the attached document.

If I open the document with Excel, and re-save it, it opens with ClosedXML fine. Just the original document refuses to open with ClosedXML.

I've included the Stack trace below, though it only really points to LoadSpreadsheetDocument.

```
Object reference not set to an instance of an object.

at ClosedXML.Excel.XLWorkbook.LoadSpreadsheetDocument(SpreadsheetDocument dSpreadsheet)
at ClosedXML.Excel.XLWorkbook.LoadSheets(String fileName)
at ClosedXML.Excel.XLWorkbook.Load(String file)
at ClosedXML.Excel.XLWorkbook..ctor(String file, XLEventTracking eventTracking)
at ClosedXML.Excel.XLWorkbook..ctor(String file)

```
Comments: Applied patch.