Fatal error when calling available_variation()

Hello,

I’ve encountered a fatal error in the current version of WPC Product Quantity Premium.
The issue occurs in wpc-product-quantity.php around line 858:

Fatal error: Uncaught Error: Call to a member function is_type() on false in
/wp-content/plugins/wpc-product-quantity-premium/wpc-product-quantity.php:858
Stack trace:
0 /wp-content/plugins/wpc-product-quantity-premium/wpc-product-quantity.php(876): WPCleverWoopq->get_quantity()
1 /wp-content/plugins/wpc-product-quantity-premium/wpc-product-quantity.php(921): WPCleverWoopq->get_type()
2 /wp-content/plugins/wpc-product-quantity-premium/wpc-product-quantity.php(1850): WPCleverWoopq->get_min()
3 /wp-includes/class-wp-hook.php(324): WPCleverWoopq->available_variation()
…

The error happens when the method available_variation() is executed in a context where the $product parameter is false or null, so calling $product->is_type() throws a fatal error.

The plugin assumes that $product is always an instance of WC_Product,
but in some contexts (for example during certain AJAX calls or variation rendering),
the woocommerce_available_variation filter can be triggered with an invalid or empty product reference.

To prevent the fatal error, a simple instance check should be added before accessing $product methods, e.g.:

if ( ! $product instanceof WC_Product ) { return $data; }

Suggested fix:

Add this validation in the following methods before using $product:

• get_type()
• get_min()
• available_variation()

This ensures compatibility with all WooCommerce contexts and prevents fatal errors when $product is not properly initialized.

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