diff --git a/Classes/Validation/DomDocumentUrlExistenceValidator.php b/Classes/Validation/DomDocumentUrlExistenceValidator.php
index 85480bf9..eb04e949 100644
--- a/Classes/Validation/DomDocumentUrlExistenceValidator.php
+++ b/Classes/Validation/DomDocumentUrlExistenceValidator.php
@@ -42,16 +42,22 @@
  */
 class DomDocumentUrlExistenceValidator extends AbstractDlfValidator
 {
+
+    /**
+     * Excluded host names separated by comma.
+     * @var array
+     */
     private array $excludeHosts;
 
     public function __construct(array $configuration = [])
     {
         parent::__construct(DOMDocument::class);
-        $this->excludeHosts = isset($configuration["excludeHosts"]) ? explode(",", $configuration["excludeHosts"]) : [];
+        $this->excludeHosts = [];
+        if (isset($configuration["excludeHosts"])) {
+            $this->excludeHosts = explode(",", $configuration["excludeHosts"]);
+        }
     }
 
-
-
     protected function isValid($value): void
     {
         foreach ($this->getDocumentUrls($value) as $url) {
@@ -69,7 +75,8 @@ protected function isValid($value): void
      */
     protected function getDocumentUrls(DOMDocument $document): array
     {
-        $tempDocument = clone $document; // do not modify original document
+        // do not modify original document
+        $tempDocument = clone $document;
         $urls = $this->getFileUrlAndRemoveFileGroups($tempDocument);
 
         // get the urls of document without file group nodes
@@ -105,7 +112,8 @@ protected function getFileUrlAndRemoveFileGroups(DOMDocument $document): array
                     $urls[] = $url;
                 }
             }
-            $hosts = []; // reset to check for every file group
+            // reset to check for every file group
+            $hosts = [];
             $fileGroup->parentNode->removeChild($fileGroup);
         }
         return $urls;
diff --git a/Tests/Unit/Validation/DomDocumentUrlExistenceValidatorTest.php b/Tests/Unit/Validation/DomDocumentUrlExistenceValidatorTest.php
index 56812e22..7192c274 100644
--- a/Tests/Unit/Validation/DomDocumentUrlExistenceValidatorTest.php
+++ b/Tests/Unit/Validation/DomDocumentUrlExistenceValidatorTest.php
@@ -51,6 +51,6 @@ protected function createValidator(): AbstractDlfValidator
     {
         // ignore all urls of fixture xml to test specifically
         $excludeHosts = 'www.loc.gov,id.loc.gov,example.com,dfg-viewer.de,www.w3.org';
-        return new DomDocumentUrlExistenceValidator(array('excludeHosts' => $excludeHosts));
+        return new DomDocumentUrlExistenceValidator(['excludeHosts' => $excludeHosts]);
     }
 }