Proper way to get array from session

I have a session which contains an item called "error", this item contains an array with the following structure:

array(1) { ["meta.featured_image"]=> string(60) "Il file meta.featured_image supera le dimensioni consentite." }

I'm trying to print the item featured_image, so I did
this:

PHP Code:

<?= session('error.meta.featured_image') ?>

But the code above returns NULL

but if I do 

PHP Code:

<?= session('error')['meta']['featured_image'] ?>

works but I need to check if the index exists to prevent error, there is no way to get the featured_image index directly in the session?