diff --git a/classes/pdf/HTMLTemplateOrderSlip.php b/classes/pdf/HTMLTemplateOrderSlip.php
index 2b02879f1e8cf..ca5a3624a74ca 100644
--- a/classes/pdf/HTMLTemplateOrderSlip.php
+++ b/classes/pdf/HTMLTemplateOrderSlip.php
@@ -131,7 +131,7 @@ public function getContent()
             }
             unset($product);
         } else {
-            $this->order->products = null;
+            $this->order->products = [];
         }
 
         if ($this->order_slip->shipping_cost == 0) {