Actors: avoid PHP warnings when trying to fetch invalid actor.

[jeherve]

Fixes CMF-356

Proposed changes:

Since get_post can return null or an int, it's best to explicitely check for a WP_Post return.

This should avoid PHP warnings like this one:

Warning: Attempt to read property "post_content" on null in /public_html/wp-content/plugins/activitypub/includes/functions.php on line 114

Other information:

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

Testing instructions:

• This should be testable on a WordPress.com sandbox, since that's where the warnings are easily repeatable (see original issue).

Changelog entry

• Automatically create a changelog entry from the details below.

Changelog Entry Details

Significance

• Patch
• Minor
• Major

Type

• Added - for new features
• Changed - for changes in existing functionality
• Deprecated - for soon-to-be removed features
• Removed - for now removed features
• Fixed - for any bug fixes
• Security - in case of vulnerabilities

Message

[Copilot]

Pull request overview

This PR fixes PHP warnings that occur when get_post() returns null by adding explicit WP_Post instance checks in three methods that fetch remote actor data.

Key Changes:

• Added instanceof \WP_Post validation after get_post() calls to prevent accessing properties on null values
• Returns consistent WP_Error objects with appropriate error codes when post retrieval fails
• Applied the fix to three methods: get_by_uri(), fetch_by_uri(), and fetch_by_acct()

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
includes/collection/class-remote-actors.php	Added explicit WP_Post type checks in three methods to prevent PHP warnings when attempting to access post properties on null values
.github/changelog/fix-post-explicit-wp-post-return	Added changelog entry documenting the patch-level fix

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Review Summary: The changes are well-implemented and consistent across all three affected methods. The explicit type checking provides a robust defense against null pointer warnings and properly returns error objects that align with the existing error handling patterns in the codebase. No issues were identified during the review.

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[jeherve]

Tests are failing for a different root cause, that should get fixed in #2724

[pfefferle]

thanks @jeherve