public function findWhereProduct(Product $product)
 {
     return $this->executeCallback(get_called_class(), __FUNCTION__, ['product' => $product->getMorphString()], function () use($product) {
         // mimic a where clause in order to properly generate the cache hash
         $this->where('product', $product->getMorphString());
         return $product->shippingPlans;
     });
 }