def _to_dict(self):
        """Return a json dictionary representing this model."""
        _dict = {}
        if hasattr(self, 'notice_id') and self.notice_id is not None:
            _dict['notice_id'] = self.notice_id
        if hasattr(self, 'created') and self.created is not None:
            _dict['created'] = datetime_to_string(self.created)
        if hasattr(self, 'document_id') and self.document_id is not None:
            _dict['document_id'] = self.document_id
        if hasattr(self, 'query_id') and self.query_id is not None:
            _dict['query_id'] = self.query_id
        if hasattr(self, 'severity') and self.severity is not None:
            _dict['severity'] = self.severity
        if hasattr(self, 'step') and self.step is not None:
            _dict['step'] = self.step
        if hasattr(self, 'description') and self.description is not None:
            _dict['description'] = self.description
        return _dict