diff --git a/src/wp-includes/functions.php b/src/wp-includes/functions.php
index 658afaad3c..6c5184f697 100644
--- a/src/wp-includes/functions.php
+++ b/src/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 ) );
 }