Icons: Reject null for the icon collection public property so it cannot silently become non-public.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: t-hamano

src/wp-includes/class-wp-icon-collections-registry.php

@@ -123,7 +123,7 @@ public function register( $collection_slug, $collection_properties ) {
 			return false;
 		}
 
-		if ( isset( $collection_properties['public'] ) && ! is_bool( $collection_properties['public'] ) ) {
+		if ( array_key_exists( 'public', $collection_properties ) && ! is_bool( $collection_properties['public'] ) ) {
 			_doing_it_wrong(
 				__METHOD__,
 				__( 'Icon collection public property must be a boolean.' ),

tests/phpunit/tests/icons/wpIconCollectionsRegistry.php

@@ -287,6 +287,7 @@ public function data_non_boolean_public_properties() {
 			'string'  => array( 'false' ),
 			'integer' => array( 0 ),
 			'array'   => array( array() ),
+			'null'    => array( null ),
 		);
 	}
 }