PHP Warnings

Hi,

Plugin version : Version 2.1.1 (FREE)

When I access to « Hummingbird » >> « Page Caching » >> « Configure » I have the following messages :

PHP Notice: Undefined index: cookies \wp-content\plugins\hummingbird-performance\admin\views\caching\page-caching-meta-box.php on line 420
PHP Warning: join(): Invalid arguments passed in \wp-content\plugins\hummingbird-performance\admin\views\caching\page-caching-meta-box.php on line 420

Can you help us ?

Thanks