code: def directory_listing_content_check(directory_path, listing):
          
          if listing:
              for sub in listing:
                  path = os.path.join(directory_path, sub['basename'])
                  if sub['class'] == 'File':
                      if not os.path.isfile(path):
                          return 'listing contains "{}" but this file could not be found on disk.'.format(path)
                  elif sub['class'] == 'Directory':
                      if not os.path.isdir(path):
                          return 'listing contains "{}" but this directory could not be found on disk'.format(path)
                      listing = sub.get('listing')
                      if listing:
                          return ConnectorManager.directory_listing_content_check(path, listing)
          return None
docs: Checks if a given listing is present under the given directory path.
  
          :param directory_path: The path to the base directory
          :param listing: The listing to check
          :return: None if no errors could be found, otherwise a string describing the error