The `WP_Sitemaps_Provider::get_sitemap_url()` method calls the PHP native `http_build_query()` function, the second parameter of which is the ''optional'' `$numeric_prefix` parameter which expects a `string`.
A parameter being optional, however, does not automatically make it nullable.
As of PHP 8.1, passing `null` to a non-nullable PHP native function will generate a deprecation notice.
In this case, this function call yielded a `http_build_query(): Passing null to parameter #2 ($numeric_prefix) of type string is deprecated` notice.
Changing the `null` to an empty string fixes this without a backward compatibility break.
This change is already covered by tests as 14 of the existing tests failed on these function calls when running the tests on PHP 8.1.
References:
* [https://www.php.net/manual/en/function.http-build-query.php PHP Manual: http_build_query()]
* [https://wiki.php.net/rfc/deprecate_null_to_scalar_internal_arg PHP RFC: Deprecate passing null to non-nullable arguments of internal functions]
Follow-up to [48470].
Props jrf.
See #53635.
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While web crawlers are able to discover pages from links within the site and from other sites, XML sitemaps supplement this approach by allowing crawlers to quickly and comprehensively identify all URLs included in the sitemap and learn other signals about those URLs using the associated metadata.
See https://make.wordpress.org/core/2020/06/10/merge-announcement-extensible-core-sitemaps/ for more details.
This feature exposes the sitemap index via `/wp-sitemap.xml` and exposes a variety of new filters and hooks for developers to modify the behavior. Users can disable sitemaps completely by turning off search engine visibility in WordPress admin.
This change also introduces a new `esc_xml()` function to escape strings for output in XML, as well as XML support to `wp_kses_normalize_entities()`.
Props Adrian McShane, afragen, adamsilverstein, casiepa, flixos90, garrett-eclipse, joemcgill, kburgoine, kraftbj, milana_cap, pacifika, pbiron, pfefferle, Ruxandra Gradina, swissspidy, szepeviktor, tangrufus, tweetythierry.
Fixes#50117.
See #3670. See #19998.
Built from https://develop.svn.wordpress.org/trunk@48072
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John Blackbourn
Sergey Biryukov
Pascal Birchler