ISTWCMS-4947: fixing undefined index error

src/Service/UWService.php

@@ -316,7 +316,12 @@ class UWService implements UWServiceInterface {
             break;
 
           case 'address':
-            $node_data['address'] = $node->$data->getValue()[0];
+            if ($node->$data->getValue()) {
+              $node_data['address'] = $node->$data->getValue()[0];
+            }
+            else {
+              $node_data['address'] = NULL;
+            }
             break;
 
           case 'author':