Map block: Prevent PHP fatal when content is empty

[tbradsha]

If the Map block receives empty content, it results in a PHP fatal. This PR returns early in that scenario.

Proposed changes:

This was discovered while monitoring a deploy:

PHP Fatal error: Uncaught ValueError: DOMDocument::loadHTML(): Argument #1 ($source) must not be empty in /wordpress/plugins/jetpack/14.3-a.5/extensions/blocks/map/map.php:159 Stack trace: #0 /wordpress/plugins/jetpack/14.3-a.5/extensions/blocks/map/map.php(159): DOMDocument->loadHTML('')

Prior to PHP 8, DOMDocument::loadHTML() would throw a deprecation notice if the source string is empty; now it gives a fatal (docs).

There's no way to reliably prevent $content from being empty, given there's an apply_filters() just before which could be used by any third-party code.

At first I wasn't sure if it was safe to just return, but looking further in code that'd be precisely what it does if $container is not truthy, which would always be case since the DOMXPath::query would not find the path in question with empty content anyway. I believe another solution would be to throw a dummy <div></div> into $content should it be empty, but that seems more hackish.

Anyway, I'm fairly confident this restores the same behavior seen in PHP <8.

Note: the line in question did have a suppression before with @ added in d9492d1, but it's unclear from the PR (#13405) or the commit message if this or some other scenario warranted it. As such, I'm leaving it in place for now. There are also some libxml_use_internal_errors() calls, but those would be applicable for normal parsing errors too, so should stay.

Other information:

• Have you written new tests for your changes, if applicable?
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Jetpack product discussion

Does this pull request change what data or activity we track or use?

Testing instructions:

I'm not sure how to reproduce this best...check my logic above?

[github-actions]

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[github-actions]

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[github-actions]

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/plugins/jetpack/extensions/blocks/map/map.php	0/120 (0.00%)	0.00%	2 💔

Full summary · PHP report · JS report