Sync: prevent deprecation warning with null values in trim_post_meta

[coder-karen]

Fixes VULCAN-56

Proposed changes:

• This PR adds a null check before calling strlen, in trim_post_meta. This prevents a PHP deprecation warning when the serialized value passed into strlen is null:

PHP Deprecated:  strlen(): Passing null to parameter #1 ($string) of type string is deprecated in /usr/local/src/jetpack-monorepo/projects/packages/sync/src/modules/class-posts.php on line 315`

• Previously, if a value was null, it would still be processed by strlen (returning a value of 0), therefore setting the meta_value to ''. We still want that to be the case - if $serialized_value is null, then set $meta_value to 'null'. By explicitly checking this first, we prevent the PHP deprecation warning as we don't run null through strlen, and we get the same results as before so as not to break any expected functionality.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

n/a

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

No.

Testing instructions:

To replicate this issue, test with trunk locally or on bleeding edge / release candidate / latest version of Jetpack on a Jurassic Ninja site using the Jetpack Beta tester plugin. Then:

• In class-posts.php, just above the changed line, set $serialized_value to null (on a site using the Jetpack Beta tester plugin you'll be looking for plugins/jetpack-dev/jetpack_vendor/automattic/jetpack-sync/src/modules/class-posts/php)
• On a new or existing post, add or update the featured image.
• Check your error logs, and you should see the deprecation warning mentioned in the PR description.

To test the fix, follow the same steps after applying the changes in this PR. You should not see the deprecation warning in your error logs.

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (Jetpack or WordPress.com Site Helper), and enable the fix/trim_post_meta-strlen-deprecation-warning branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack fix/trim_post_meta-strlen-deprecation-warning

bin/jetpack-downloader test jetpack-mu-wpcom-plugin fix/trim_post_meta-strlen-deprecation-warning

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

Thank you for your PR!

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[jp-launch-control]

Code Coverage Summary

This PR did not change code coverage!

That could be good or bad, depending on the situation. Everything covered before, and still is? Great! Nothing was covered before? Not so great. 🤷

Full summary · PHP report · JS report

[fgiannar]

Many thanks for the fix, Karen! LGTM 🚢