public static function normalize($data)
    {
        $result = [];

        foreach ($data as $key => $value) {
            if (!is_int($key)) {
                $result[$key] = $value;
                continue;
            }
            if (!is_scalar($value)) {
                throw new Exception("Invalid array format, a value can't be normalized");
            }
            $result[$value] = null;
        }
        return $result;
    }