In _wp_json_convert_string(), when $use_mb is false, perhaps pass a variable that actually exists to wp_check_invalid_utf8().

Introduced in [30055].
See #30224.

Built from https://develop.svn.wordpress.org/trunk@30162


git-svn-id: http://core.svn.wordpress.org/trunk@30162 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/functions.php

@@ -2739,7 +2739,7 @@ function _wp_json_convert_string( $string ) {
 			return mb_convert_encoding( $string, 'UTF-8', 'UTF-8' );
 		}
 	} else {
-		return wp_check_invalid_utf8( $data, true );
+		return wp_check_invalid_utf8( $string, true );
 	}
 }