Cannot add to cart after plugin to intercept

Question

I am trying to intercept add to cart button.

What I intend to do:
If customer is not logged in, throw error message. Else if customer is logged in, add item to cart.

I did it in following way. I got the error message Cannot add to cart. as expector for customer that is not logged in. But I can't get user to add the product if the customer is logged in. I get the error message We can't add this item to your shopping cart right now..

What am I doing it wrong? Note that I can add the particular product to cart if i commented out the logic in this plugin.

============================================================================= Note updated code as advise. It seems like can't get customer session with following code. Everything works correctly if i commented out the customer session \Magento\Customer\Model\Session and related code to check if customer is log in.

use Magento\Framework\Exception\LocalizedException;

class Cart
{
    protected $session;

    public function __construct(
        \Magento\Customer\Model\Session $session
    ) {
        $this->session = $session;
    }

    public function beforeAddProduct(
        \Magento\Checkout\Model\Cart $subject,
        $productInfo,
        $requestInfo) {
        if (!$this->session->isLoggedIn()) {
            throw new LocalizedException(__('Cannot add to cart.'));
            return [$productInfo, $requestInfo];
        }
       return [$productInfo, $requestInfo];
    }
}

Answer 1

For checking customer logged in or not, use Magento\Customer\Model\Session