Fix template date and modified return value for file templates

[ntsekouras]

Trac ticket: https://core.trac.wordpress.org/ticket/65728

Follow up of: https://core.trac.wordpress.org/ticket/65049

Backports: WordPress/gutenberg#80733

As noted here: WordPress/gutenberg#77134 (comment), the new date field for templates and template parts can return false for file templates.

In practice this doesn't cause any errors but still the returned value should match the declared type (string|null).

With that comment I realized that modified has the exact same problem for many versions (since 6.3).

We should update the type of modified to be the same with date to string|null and not return false for file templates.

Testing instructions

1. Log in and ensure you have a block theme enabled
2. Test the templates REST endpoint in dev tools: const templates = await wp.apiFetch( { path: '/wp/v2/templates?per_page=100' } );. Then inspect templates
3. Observe that date and modified is null for file templates.

Use of AI Tools

Opus 5 with direction, changes and review

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Pull request overview

This PR ensures the REST API response for templates exposes a null date for file-backed templates, instead of the false value produced by mysql_to_rfc3339() for empty input—aligning the runtime value with the declared schema type (string|null).

Changes:

• Normalize date in WP_REST_Templates_Controller::prepare_item_for_response() to return null when the template has no date (file-backed templates).
• Add a PHPUnit REST API test asserting date is null for a file-backed template.
• Minor schema array formatting adjustment (alignment) near the date property.

Reviewed changes

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

File	Description
tests/phpunit/tests/rest-api/wpRestTemplatesController.php	Adds regression test to ensure file-backed templates expose date: null via the REST API.
src/wp-includes/rest-api/endpoints/class-wp-rest-templates-controller.php	Prevents date from being serialized as false by returning null when no date exists, matching the schema’s allowed types.

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Props ntsekouras, tyxla.

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Pull request overview

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