docs: def _to_dict(self):
          """Return a json dictionary representing this model."""
          _dict = {}
          if hasattr(self, 'trait_id') and self.trait_id is not None:
              _dict['trait_id'] = self.trait_id
          if hasattr(self, 'name') and self.name is not None:
              _dict['name'] = self.name
          if hasattr(self, 'category') and self.category is not None:
              _dict['category'] = self.category
          if hasattr(self, 'percentage') and self.percentage is not None:
              _dict['percentage'] = self.percentage
          return _dict