Fixed deprecated method usage in HelperController

Controller/HelperController.php

@@ -252,7 +252,7 @@ class HelperController
             return new JsonResponse(array('status' => 'KO', 'message' => 'The field cannot be edit, editable option must be set to true'));
         }
 
-        $propertyAccessor = PropertyAccess::getPropertyAccessor();
+        $propertyAccessor = PropertyAccess::createPropertyAccessor();
         $propertyPath     = new PropertyPath($field);
 
         // If property path has more than 1 element, take the last object in order to validate it