Merge remote-tracking branch 'origin/ACP2E-4324' into PR_2025_11_20_flowers

Author: thiaramus

app/code/Magento/PageCache/Model/App/Response/HttpPlugin.php

@@ -43,8 +43,7 @@ public function beforeSendResponse(HttpResponse $subject)
 
         $currentVary = $this->context->getVaryString();
         $varyCookie = $this->request->get(HttpResponse::COOKIE_VARY_STRING);
-        if ($currentVary !== $varyCookie) {
-            //prevent caching with the old vary cookie
+        if (isset($varyCookie) && ($currentVary !== $varyCookie)) {
             $subject->setNoCacheHeaders();
         }
         $subject->sendVary();

app/code/Magento/PageCache/Test/Unit/Model/App/Response/HttpPluginTest.php

@@ -92,4 +92,16 @@ public function testBeforeSendResponseVaryMismatch()
 
         $this->httpPlugin->beforeSendResponse($responseMock);
     }
+
+    public function testBeforeSendResponseVaryNotSet()
+    {
+        /** @var HttpResponse|MockObject $responseMock */
+        $this->context->expects($this->any())->method('getVaryString')->willReturn('currentVary');
+        $this->request->expects($this->any())->method('get')->willReturn(null);
+        /** @var HttpResponse|MockObject $responseMock */
+        $responseMock = $this->createMock(HttpResponse::class);
+        $responseMock->expects($this->never())->method('setNoCacheHeaders');
+        $responseMock->expects($this->once())->method('sendVary');
+        $this->httpPlugin->beforeSendResponse($responseMock);
+    }
 }