protected function _stringifyExpressions($expressions, $generator, $wrap = true)
    {
        $result = [];
        foreach ($expressions as $k => $expression) {
            if ($expression instanceof ExpressionInterface) {
                $value = $expression->sql($generator);
                $expression = $wrap ? '(' . $value . ')' : $value;
            }
            $result[$k] = $expression;
        }

        return $result;
    }