Fix core tests

src/Control/Middleware/ChangeDetectionMiddleware.php

@@ -25,6 +25,9 @@ class ChangeDetectionMiddleware implements HTTPMiddleware
     {
         /** @var HTTPResponse $response */
         $response = $delegate($request);
+        if (!$response) {
+            return null;
+        }
 
         // Ignore etag for no-store
         $cacheControl = $response->getHeader('Cache-Control');

src/Control/Middleware/HTTPCacheControlMiddleware.php

@@ -43,6 +43,9 @@ class HTTPCacheControlMiddleware implements HTTPMiddleware, Resettable
         } catch (HTTPResponse_Exception $ex) {
             $response = $ex->getResponse();
         }
+        if (!$response) {
+            return null;
+        }
 
         // Update state based on current request and response objects
         $this->augmentState($request, $response);