if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
header('HTTP/1.1 304 Not Modified');
header("Last-Modified: " . gmdate("D, d M Y H:i:s", time()) . " GMT");
- header('Etag: ' . $_SERVER['HTTP_IF_NONE_MATCH']);
+ if (!empty($_SERVER['HTTP_IF_NONE_MATCH'])) {
+ header('Etag: ' . $_SERVER['HTTP_IF_NONE_MATCH']);
+ }
header("Expires: " . gmdate("D, d M Y H:i:s", time() + (31536000)) . " GMT");
header("Cache-Control: max-age=31536000");
if (function_exists('header_remove')) {