Apple Configurator: Redemption Codes Not Imported – The spreadsheet provided has redemption codes for "(null)."

When importing a Volume Purchase Plan (VPP) spreadsheet into Apple Configurator 1.2.1, you may see a message like the following: "The spreadsheet provided has redemption codes for "(null)." Please provide a spreadsheet with codes for 'Numbers.'"  (Where "Numbers" is the name of the application for which you are importing codes.)