refs #21067 [finc] bugfix in getItemNotes

* adds cast to array for index 'about'

module/finc/src/finc/ILS/Driver/FincLibero.php

@@ -676,11 +676,12 @@ class FincLibero extends FincILS implements TranslatorAwareInterface
     {
         // add all item specific information from DAIA field about to item_notes
         // (https://intern.finc.info/issues/7863)
+        $about = $item['about'] ?? [];
         return array_unique(
             array_merge(
                 (array)$return['status'],
                 $return['item_notes'],
-                $item['about'] ?? []
+                (array) $about
             )
         );
     }