add query to return list users in json

src/Application/Actions/Search/ListUsersJson.php

@@ -30,7 +30,8 @@ class ListUsersJson extends Action
 
         $parsedRequestBody = (array)$this->request->getParsedBody();
 
-        $search =  $this->request->getQueryParams()['q'];
+        $queryParams = $this->request->getQueryParams();
+        $search = isset($queryParams['q']) ? $queryParams['q'] : '';
         
         $users_query = $this->userRepository->createQueryBuilder('u');
         $users_list = $users_query