Error message

Warning: count() [function.count.php]: Parameter must be an array or an object that implements Countable in GuzzleHttp\Handler\CurlFactory->release() (line 67 of /home/atticind/www/atticindependent.ch/drupal/sites/all/libraries/mailchimp/vendor/guzzlehttp/guzzle/src/Handler/CurlFactory.php).