Only get purchase note if product exists

Fixes #10726

templates/order/order-details.php

@@ -13,7 +13,7 @@
  * @see 	http://docs.woothemes.com/document/template-structure/
  * @author  WooThemes
  * @package WooCommerce/Templates
- * @version 2.5.3
+ * @version 2.6.0
  */
 
 if ( ! defined( 'ABSPATH' ) ) {
@@ -37,15 +37,14 @@ $show_customer_details = is_user_logged_in() && $order->get_user_id() === get_cu
 		<?php
 			foreach( $order->get_items() as $item_id => $item ) {
 				$product = apply_filters( 'woocommerce_order_item_product', $order->get_product_from_item( $item ), $item );
-				$purchase_note = get_post_meta( $product->id, '_purchase_note', true );
 
 				wc_get_template( 'order/order-details-item.php', array(
-					'order'					=> $order,
-					'item_id'				=> $item_id,
-					'item'					=> $item,
-					'show_purchase_note'	=> $show_purchase_note,
-					'purchase_note'			=> $purchase_note,
-					'product'				=> $product,
+					'order'			     => $order,
+					'item_id'		     => $item_id,
+					'item'			     => $item,
+					'show_purchase_note' => $show_purchase_note,
+					'purchase_note'	     => $product ? get_post_meta( $product->id, '_purchase_note', true ) : '',
+					'product'	         => $product,
 				) );
 			}
 		?>