code: def validate_extra_link(self, extra_link):
      
      if EXTRA_LINK_NAME_KEY not in extra_link or EXTRA_LINK_FORMATTER_KEY not in extra_link:
        raise Exception("Invalid extra.links format. " +
                        "Extra link must include a 'name' and 'formatter' field")
  
      self.validated_formatter(extra_link[EXTRA_LINK_FORMATTER_KEY])
      return extra_link
docs: validate extra link