docs: def _to_dict(self):
          """Return a json dictionary representing this model."""
          _dict = {}
          if hasattr(self, 'authors') and self.authors is not None:
              _dict['authors'] = [x._to_dict() for x in self.authors]
          if hasattr(self,
                     'publication_date') and self.publication_date is not None:
              _dict['publication_date'] = self.publication_date
          if hasattr(self, 'title') and self.title is not None:
              _dict['title'] = self.title
          if hasattr(self, 'image') and self.image is not None:
              _dict['image'] = self.image
          if hasattr(self, 'feeds') and self.feeds is not None:
              _dict['feeds'] = [x._to_dict() for x in self.feeds]
          return _dict