PHP Deprecated: Sabberworm\CSS\CSSList\Document::render(): Implicitly marking parameter $oOutputFormat as nullable

[costasovo]

I'm getting a PHP Warning on PHP 8.4.

PHP Deprecated: Sabberworm\CSS\CSSList\Document::render(): Implicitly marking parameter $oOutputFormat as nullable is deprecated, the explicit nullable

[22-Jul-2025 15:57:39 UTC] PHP Deprecated:  Sabberworm\CSS\CSSList\Document::render(): Implicitly marking parameter $oOutputFormat as nullable is deprecated, the explicit nullable type must be used instead in /public_html/wp-content/plugins/woocommerce/vendor/sabberworm/php-css-parser/src/CSSList/Document.php on line 158 

I see the code is already updated in the main branch. We are currently using v8.9.0 installed as a dependency of Emogrifier. I see that the fix is not present in v8.x branch. Are there any plans to get these fixes into a v8 release?

[JakeQZ]

Hi @costasovo,

The 8.x branch tries to support PHP versions from 5.6 to 8.4. This is becoming increasingly difficult because of this specific issue. It may not be possible to have functions with nullable arguments that work across this wide a range of PHP versions without a deprecation warning (which will inevitably be an error in PHP 8.5). @oliverklee battled with backporting the changes to support PHP 8.4, and may be able to shed more light. (I would have expected a PHPUnit error from the notice, but maybe we silenced this.)

Are there any plans to get these fixes into a v8 release?

No, since it is probably impossible.

But we do plan to release 9.0 very soon (maybe a week or so - #1328). This will require a minumum PHP version of 7.2.

[oliverklee]

This is strange. I thought we had fixed this with #746 for version 8.7.0.

@costasovo Could you please re-check that

1. you're on version 8.9.0 (and not an earlier release)
2. the signature of Document::render() looks like this on the system that throws the warning?

public function render($oOutputFormat = null)

… and then report back? Thanks!

[costasovo]

Hi @oliverklee,

The warning was logged from 8.7.0. We updated to 8.9.0 just recently, and it has not been released. Sorry about the confusion.

The signature is:

    /**
     * Overrides `render()` to make format argument optional.
     *
     * @param OutputFormat|null $oOutputFormat
     *
     * @return string
     */
    public function render($oOutputFormat = null)

This seems to be the same in 8.7.0 and 8.9.0.

If I understand this post correctly, is the code that triggers the warning in PHP 8.4.

[oliverklee]

@costasovo In that post under Recommended Changes > Dropping parameter type, it is listed what we did for the 8.x branch:

Applications and PHP libraries that must run on all PHP versions from PHP 7.0 or PHP 5 all the way to PHP 8.4 cannot use the nullable types because nullable types are only supported on PHP 7.1 and later.

Although highly discouraged, removing the type declaration in the parameter, and then checking the type from inside the function is a last-resort way to avoid the deprecation notice while keeping the code compatible with PHP 7.0 and later.

I honestly have no idea why our code creates that warning with PHP 8.4 on your system.

[JakeQZ]

There is now a 9.0 release which will address the issue - closing.