old_contents: class BadUrlException(Exception):
      pass
  
  
  class NoFormDataException(Exception):
      pass
  
new_contents: class BadUrlException(Exception):
      pass
  
  
  class NoFormDataException(Exception):
      pass
  
  
  class FileGoneException(Exception):
      pass
  
  
  class InvalidXMLException(Exception):
      pass
  
subject: Add missing exception classes