Return a json dictionary representing this model.

def _to_dict(self):
        """Return a json dictionary representing this model."""
        _dict = {}
        if hasattr(self,
                   'customization_id') and self.customization_id is not None:
            _dict['customization_id'] = self.customization_id
        if hasattr(self, 'name') and self.name is not None:
            _dict['name'] = self.name
        if hasattr(self, 'language') and self.language is not None:
            _dict['language'] = self.language
        if hasattr(self, 'owner') and self.owner is not None:
            _dict['owner'] = self.owner
        if hasattr(self, 'created') and self.created is not None:
            _dict['created'] = self.created
        if hasattr(self, 'last_modified') and self.last_modified is not None:
            _dict['last_modified'] = self.last_modified
        if hasattr(self, 'description') and self.description is not None:
            _dict['description'] = self.description
        if hasattr(self, 'words') and self.words is not None:
            _dict['words'] = [x._to_dict() for x in self.words]
        return _dict