diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index a7a92e4dd..2e2253269 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" bootstrap="tests/bootstrap.php" colors="true" convertWarningsToExceptions="false" convertNoticesToExceptions="false" convertErrorsToExceptions="false" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" bootstrap="tests/bootstrap.php" colors="true" convertWarningsToExceptions="true" convertNoticesToExceptions="false" convertErrorsToExceptions="true" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
   <coverage>
     <include>
       <directory suffix=".php">src</directory>
diff --git a/src/Middleware/AuthTokenMiddleware.php b/src/Middleware/AuthTokenMiddleware.php
index b10cf9bff..798766efa 100644
--- a/src/Middleware/AuthTokenMiddleware.php
+++ b/src/Middleware/AuthTokenMiddleware.php
@@ -132,7 +132,7 @@ private function addAuthHeaders(RequestInterface $request)
         ) {
             $token = $this->fetcher->fetchAuthToken();
             $request = $request->withHeader(
-                'authorization', 'Bearer ' . ($token['access_token'] ?? $token['id_token'])
+                'authorization', 'Bearer ' . ($token['access_token'] ?? $token['id_token'] ?? '')
             );
         } else {
             $headers = $this->fetcher->updateMetadata($request->getHeaders(), null, $this->httpHandler);