Null Reference on XlsIO.AddCopy()

We just updated to 12.3.0.36 of Syncfusion and we started getting a Null Reference Error on our Worksheet.AddCopy calls.  I'm sure it's because we are doing something wrong and it just wasn't causing a problem before.  We do have code that messes around with IName.Delete().  But in the earlier version of XlsIO things ran OK. 

Stack Trace:

Object reference not set to an instance of an object.

   at Syncfusion.XlsIO.Implementation.Collections.WorksheetNamesCollection.FillFrom(WorksheetNamesCollection sourceNames, IDictionary hashNewWorksheetNames, Dictionary`2 dicNewNameIndexes, ExcelNamesMergeOptions option, Dictionary`2 hashExternSheetIndexes)
   at Syncfusion.XlsIO.Implementation.WorksheetImpl.CopyNames(WorksheetImpl basedOn, Dictionary`2 hashNewSheetNames, Dictionary`2 hashNewNameIndexes, Dictionary`2 hashExternSheetIndexes)
   at Syncfusion.XlsIO.Implementation.WorksheetImpl.CopyFrom(WorksheetImpl worksheet, Dictionary`2 hashStyleNames, Dictionary`2 hashWorksheetNames, Dictionary`2 dicFontIndexes, ExcelWorksheetCopyFlags flags, Dictionary`2 hashExtFormatIndexes, Dictionary`2 hashNameIndexes, Dictionary`2 hashExternSheets)
   at Syncfusion.XlsIO.Implementation.Collections.WorksheetsCollection.AddCopy(IWorksheet sheet, ExcelWorksheetCopyFlags flags, Boolean isLocal)
   at Syncfusion.XlsIO.Implementation.Collections.WorksheetsCollection.AddCopy(IWorksheet sheet, ExcelWorksheetCopyFlags flags)
   at Syncfusion.XlsIO.Implementation.Collections.WorksheetsCollection.AddCopy(IWorksheet sheet)

Can anyone point me in the right direction as to what we might be doing wrong to cause XlsIO to Exception when we call AddCopy()?  Thanks