protected function getContentType($format)
    {
        // Check if it's already MIME
        if (\Jasny\str_contains($format, '/')) {
            return $format;
        }
        
        $repository = new ApacheMimeTypes();
        $mime = $repository->findType($format);

        if (!isset($mime)) {
            throw new \UnexpectedValueException("Format '$format' doesn't correspond with a MIME type");
        }
        
        return $mime;
    }