Index: src/wp-admin/includes/post.php
===================================================================
--- src/wp-admin/includes/post.php	(revision 55757)
+++ src/wp-admin/includes/post.php	(working copy)
@@ -1555,11 +1555,11 @@
 	 * @since 2.9.0
 	 * @since 4.4.0 Added `$post` parameter.
 	 *
-	 * @param string  $return    Sample permalink HTML markup.
-	 * @param int     $post_id   Post ID.
-	 * @param string  $new_title New sample permalink title.
-	 * @param string  $new_slug  New sample permalink slug.
-	 * @param WP_Post $post      Post object.
+	 * @param string      $return    Sample permalink HTML markup.
+	 * @param int         $post_id   Post ID.
+	 * @param string|null $new_title New sample permalink title.
+	 * @param string|null $new_slug  New sample permalink slug.
+	 * @param WP_Post $post Post object.
 	 */
 	$return = apply_filters( 'get_sample_permalink_html', $return, $post->ID, $new_title, $new_slug, $post );