docs: def record_file_factory(pid, record, filename):
      """Get file from a record.
  
      :param pid: Not used. It keeps the function signature.
      :param record: Record which contains the files.
      :param filename: Name of the file to be returned.
      :returns: File object or ``None`` if not found.
      """
      try:
          if not (hasattr(record, 'files') and record.files):
              return None
      except MissingModelError:
          return None
  
      try:
          return record.files[filename]
      except KeyError:
          return None