Executes the query if self.query_set_obj is set
        :return: The result of aggregation query

def execute(self):
        """
        Executes the query if self.query_set_obj is set
        :return: The result of aggregation query
        """
        if self.query_set_obj is None:
            return []

        if self.is_mongoengine:
            result = self.query_set_obj.aggregate(*self.get_query())
        else:
            result = self.query_set_obj.aggregate(self.get_query())

        if IS_PYMONGO_3:
            result = list(result)
        else:
            result = result.get('result')
        if result:
            return result
        return []