code: def nrfa_metadata():
      
      result = {
          'url': config.get('nrfa', 'url', fallback=None) or None,  # Empty strings '' become None
          'version': config.get('nrfa', 'version', fallback=None) or None,
          'published_on': config.get_datetime('nrfa', 'published_on', fallback=None) or None,
          'downloaded_on': config.get_datetime('nrfa', 'downloaded_on', fallback=None) or None
      }
      return result
docs: Return metadata on the NRFA data.
  
      Returned metadata is a dict with the following elements:
  
      - `url`: string with NRFA data download URL
      - `version`: string with NRFA version number, e.g. '3.3.4'
      - `published_on`: datetime of data release/publication (only month and year are accurate, rest should be ignored)
      - `downloaded_on`: datetime of last download
  
      :return: metadata
      :rtype: dict