Taxonomy: Document that the `get_terms` filter can have `null` for `$taxonomies`.

The `get_terms` filter currently documents that the filter passes an array as both the first and second parameters, which is normally true, except that the second can be `null` when not specified.  This change updates the filter's docblock to indicate that the second parameter can also be of a `null` type.

Props dd32, audrasjb, mukesh27.
Fixes #54222.
Built from https://develop.svn.wordpress.org/trunk@52131


git-svn-id: http://core.svn.wordpress.org/trunk@51723 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/taxonomy.php

@@ -1330,7 +1330,7 @@ function get_terms( $args = array(), $deprecated = '' ) {
 	 * @since 4.6.0 Added the `$term_query` parameter.
 	 *
 	 * @param array         $terms      Array of found terms.
-	 * @param array         $taxonomies An array of taxonomies.
+	 * @param array|null    $taxonomies An array of taxonomies if known.
 	 * @param array         $args       An array of get_terms() arguments.
 	 * @param WP_Term_Query $term_query The WP_Term_Query object.
 	 */

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-52130';
+$wp_version = '5.9-alpha-52131';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.