:return: response stats dict

def get(self):
        """
        :return: response stats dict
        """
        stats = {}
        if self.start_date is not None:
            stats["start_date"] = self.start_date
        if self.end_date is not None:
            stats["end_date"] = self.end_date
        if self.aggregated_by is not None:
            stats["aggregated_by"] = self.aggregated_by
        if self.sort_by_metric is not None:
            stats["sort_by_metric"] = self.sort_by_metric
        if self.sort_by_direction is not None:
            stats["sort_by_direction"] = self.sort_by_direction
        if self.limit is not None:
            stats["limit"] = self.limit
        if self.offset is not None:
            stats["offset"] = self.offset
        if self.categories is not None:
            stats['categories'] = [category.get() for category in
                                   self.categories]
        return stats