[dannflorea]

Trac ticket: https://core.trac.wordpress.org/ticket/66377

What

When a single meta key has nothing stored, WP_REST_Meta_Fields::update_value() validated the empty string returned by get_metadata() before a null reset. For boolean, integer, number and enum keys that fails, so the request was rejected with a 500 rest_invalid_stored_value even though nothing was stored.

This reads the current value with get_metadata_raw(), which returns null when no row exists, and only validates when there is a stored value. A stored value that fails the schema, including a stored empty string, is still protected.

This also fixes echoing back comment meta: the core _wp_note_status key (enum, no default) is returned as null when unset, and sending it back previously failed with a 500.

Tests

• test_set_value_to_null_with_nothing_stored: null for unset boolean, integer, number and enum keys returns 200 and creates no row.
• test_set_value_to_null_with_invalid_empty_string_stored: a stored empty string on a boolean key is still protected (500, row kept).
• test_update_comment_with_meta_echoed_back_from_response: updating a comment with the meta from its own GET response returns 200.

Testing instructions

1. Register register_post_meta( 'post', 'repro_flag', array( 'type' => 'boolean', 'single' => true, 'show_in_rest' => true ) );
2. On a post without that key, POST /wp/v2/posts/<id> with {"meta":{"repro_flag":null}}.
3. Before: 500 rest_invalid_stored_value. After: 200.

Verified with WordPress Playground (trunk nightly, PHP 8.3). I did not run PHPUnit locally; relying on CI.

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Props maxdevagency, westonruter.

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[westonruter]

In the case of null, get_metadata() falls back to get_metadata_default(). So this means that the fallback value doesn't need to be obtained here, since the null case is checked. So this seems right to me.

[dannflorea]

Thanks for the review, @westonruter! I've applied all the type suggestions. And thanks for confirming the get_metadata_raw() reasoning: since the null case is handled, the default fallback isn't needed there.