Ticket #55420: author-template.patch

wp-includes/author-template.php

@@ -101 +101 @@
                  *
                  * @param string $display_name The author's display name.
                  */
-                return apply_filters( 'the_modified_author', $last_user->display_name );
+                return apply_filters( 'the_modified_author', $last_user ? $last_user->display_name : '' );
         }
 }