bug #45631 [HttpFoundation] Fix PHP 8.1 deprecation in Response::isNotModified (HypeMC)

This PR was merged into the 4.4 branch.

Discussion
----------

[HttpFoundation] Fix PHP 8.1 deprecation in `Response::isNotModified`

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

If an `If-None-Match` header is provided in the request and there's no `ETag` header in the response, the following deprecation notice occurs on PHP 8.1 in `Response::isNotModified`:

```
Deprecated: strncmp(): Passing null to parameter #1 ($string1) of type string is deprecated
```

Commits
-------

b909acf2ee [HttpFoundation] Fix PHP 8.1 deprecation in isNotModified

Author: fabpot

Response.php

@@ -1079,8 +1079,7 @@ public function isNotModified(Request $request): bool
         $lastModified = $this->headers->get('Last-Modified');
         $modifiedSince = $request->headers->get('If-Modified-Since');
 
-        if ($ifNoneMatchEtags = $request->getETags()) {
-            $etag = $this->getEtag();
+        if (($ifNoneMatchEtags = $request->getETags()) && (null !== $etag = $this->getEtag())) {
             if (0 == strncmp($etag, 'W/', 2)) {
                 $etag = substr($etag, 2);
             }

Tests/ResponseTest.php

@@ -284,6 +284,20 @@ public function testIsNotModifiedIfModifiedSinceAndEtagWithoutLastModified()
         $this->assertFalse($response->isNotModified($request));
     }
 
+    public function testIfNoneMatchWithoutETag()
+    {
+        $request = new Request();
+        $request->headers->set('If-None-Match', 'randomly_generated_etag');
+
+        $this->assertFalse((new Response())->isNotModified($request));
+
+        // Test wildcard
+        $request = new Request();
+        $request->headers->set('If-None-Match', '*');
+
+        $this->assertFalse((new Response())->isNotModified($request));
+    }
+
     public function testIsValidateable()
     {
         $response = new Response('', 200, ['Last-Modified' => $this->createDateTimeOneHourAgo()->format(\DATE_RFC2822)]);