Return a json dictionary representing this model.

def _to_dict(self):
        """Return a json dictionary representing this model."""
        _dict = {}
        if hasattr(self, 'description') and self.description is not None:
            _dict['description'] = self.description
        if hasattr(self,
                   'destination_field') and self.destination_field is not None:
            _dict['destination_field'] = self.destination_field
        if hasattr(self, 'source_field') and self.source_field is not None:
            _dict['source_field'] = self.source_field
        if hasattr(self, 'overwrite') and self.overwrite is not None:
            _dict['overwrite'] = self.overwrite
        if hasattr(self,
                   'enrichment_name') and self.enrichment_name is not None:
            _dict['enrichment'] = self.enrichment_name
        if hasattr(self, 'ignore_downstream_errors'
                  ) and self.ignore_downstream_errors is not None:
            _dict['ignore_downstream_errors'] = self.ignore_downstream_errors
        if hasattr(self, 'options') and self.options is not None:
            _dict['options'] = self.options._to_dict()
        return _dict