fix client compile error

components/availability/AvailabilityForm.js

@@ -25,7 +25,8 @@ export default function AvailabilityForm({ publisherId, existingItems, inline, o
     indexUrl: "/cart/availabilities"
   };
 
-  existingitems = existingitems || [];
+  //coalsce existingItems to empty array
+  existingItems = existingItems || [];
 
   const [editMode, setEditMode] = useState(existingItems.length > 0);
   const [publisher, setPublisher] = useState({ id: publisherId });