private function buildSubclauseInnerQuery($subclause, Builder $query)
    {
        if ($subclause['require_array']) {
            return $this->buildRequireArrayQuery($subclause, $query);
        }

        if ($subclause['operator'] == 'NULL' || $subclause['operator'] == 'NOT NULL') {
            return $this->buildSubclauseWithNull($subclause, $query, ($subclause['operator'] == 'NOT NULL' ? true : false));
        }

        return $this->buildRequireNotArrayQuery($subclause, $query);
    }