The "spans" attribute is not required in the "row" element. Source of information:https://msdn.microsoft.com/en-us/library/office/documentformat.openxml.spreadsheet.row.aspx

If we create a Google Sheets spreadsheet and download it as XLSX, then the "spans" attributes do not appear in the "row" elements of the worksheet.

Attached is a test xlsx file, which causes the "Cannot read property 'split' of undefined" error when trying to read it with the exceljs package.
test-issue-163.xlsx