Fix some php warnings

CRM/Stripe/Api.php

@@ -53,8 +53,11 @@ class CRM_Stripe_Api {
             return self::formatDate($stripeObject->created);
 
           case 'invoice_id':
+            if (!isset($stripeObject->invoice)) {
+              return '';
+            }
             // Handle both "expanded" and "collapsed" response
-            if (is_object($stripeObject->invoice)) {
+            elseif (is_object($stripeObject->invoice)) {
               return (string) $stripeObject->invoice->id;
             }
             else {

managed/stripecustomdata.mgd.php

@@ -13,7 +13,10 @@ $customGroup = \Civi\Api4\CustomGroup::get(FALSE)
   ->addWhere('name', '=', 'Payment_details')
   ->execute()
   ->first();
-if (!empty($customGroup)) {
+if (empty($customGroup)) {
+  return [];
+}
+else {
   return [
     [
       'name' => 'CustomGroup_Payment_details_CustomField_available_on',
@@ -184,4 +187,4 @@ if (!empty($customGroup)) {
       ],
     ],
   ];
-}
\ No newline at end of file
+}