General: Ensure `get_tag_regex()` always returns a string, to match the documented value.

Props subrataemfluence.
Fixes #45643.
Built from https://develop.svn.wordpress.org/trunk@47430


git-svn-id: http://core.svn.wordpress.org/trunk@47217 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/functions.php

@@ -6548,7 +6548,7 @@ function wp_auth_check( $response ) {
  */
 function get_tag_regex( $tag ) {
 	if ( empty( $tag ) ) {
-		return;
+		return '';
 	}
 	return sprintf( '<%1$s[^<]*(?:>[\s\S]*<\/%1$s>|\s*\/>)', tag_escape( $tag ) );
 }

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.5-alpha-47429';
+$wp_version = '5.5-alpha-47430';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.