Fix warning in PhP 8

Author: julescournut

Config/module.xml

@@ -17,7 +17,7 @@
         <language>en_US</language>
         <language>fr_FR</language>
     </languages>
-    <version>2.0.0</version>
+    <version>2.0.1</version>
     <authors>
         <author>
             <name>Vincent Lopes-Vicente</name>

templates/backOffice/default/PayPlugModule/order_pay_plug.html

@@ -123,7 +123,7 @@ <h4>{intl l="PayPlug order data"  d='payplugmodule.bo.default'}</h4>
         <input type="hidden" name="{$name}" value="{$order_id}">
     {/form_field}
     {form_field form=$form field="refund_amount"}
-        <input id="refund_amount" type="hidden" name="{$name}" value="{$orderTotalAmount}">
+        <input id="refund_amount" type="hidden" name="{$name}" value="{$orderTotalAmount|default:null}">
     {/form_field}
     {/form}
 {/capture}