code: def validate_optional_str_fields(self, messages):
          
          FIELDS = [
              'file_name',
              'version',
              'homepage',
              'source_info',
              'summary',
              'description'
          ]
          messages = self.validate_str_fields(FIELDS, True, messages)
  
          return messages
docs: Fields marked as optional and of type string in class
          docstring must be of a type that provides __str__ method.