[BUGFIX] Undefined array key "contentSecurityPolicies"

If the 'contentSecurityPolicies' value is not filled properly
in the site configuration, the call to
$site->getConfiguration()['contentSecurityPolicies'] will fail.
The access should we guarded with a null coalescing operator.

Resolves: #104873
Releases: main, 12.4
Change-Id: Ie49a25d8ca9a194629c4a389b17b299091d44031
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85977


Reviewed-by: Garvin Hicking <gh@faktor-e.de>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Garvin Hicking <gh@faktor-e.de>
Reviewed-by: Benni Mack <benni@typo3.org>

typo3/sysext/core/Classes/Security/ContentSecurityPolicy/MutationRepository.php

@@ -114,7 +114,7 @@ final class MutationRepository
             $scopedTarget = $this->provideScopeInMap($scope, $this->resolvedMutations);
             // fetch site-specific `enforce` and/or `report` disposition configuration
             $dispositionMap = $this->dispositionMapFactory->buildDispositionMap(
-                $site->getConfiguration()['contentSecurityPolicies']
+                $site->getConfiguration()['contentSecurityPolicies'] ?? []
             );
             /**
              * @var Disposition $disposition

typo3/sysext/frontend/Classes/Middleware/ContentSecurityPolicyHeaders.php

@@ -51,7 +51,7 @@ final readonly class ContentSecurityPolicyHeaders implements MiddlewareInterface
     {
         $site = $request->getAttribute('site');
         $dispositionMap = $this->dispositionMapFactory->buildDispositionMap(
-            $site instanceof Site ? $site->getConfiguration()['contentSecurityPolicies'] : []
+            $site instanceof Site ? ($site->getConfiguration()['contentSecurityPolicies'] ?? []) : []
         );
         // return early in case CSP shall not be used
         if ($dispositionMap->keys() === []) {