Fix Laravel Cache storage: set empty string als default value

[herpaderpaldent]

By default cache return null if key is not present.

The current implementation will cause the following error notice: PHP Deprecated: unserialize(): Passing null to parameter #1 ($data) of type string is deprecated in /var/www/html/vendor/kevinrob/guzzle-cache-middleware/src/Storage/LaravelCacheStorage.php on line 32

By setting an empty string as default,unserialisewill no longer throw the error notice