protected function createAggregateQueryWithContentTypeFilter($contentType)
    {
        $qa = $this->createAggregationQuery();

        if ($contentType) {
            $qa->match(array('contentType' => $contentType));
        }

        return $qa;
    }
protected function createAggregateQueryWithContentTypeFilter($contentType)
    {
        $qa = $this->createAggregationQuery();

        if ($contentType) {
            $qa->match(array('contentType' => $contentType));
        }

        return $qa;
    }
@param $contentType

@return \Solution\MongoAggregation\Pipeline\Stage