Issue #3239552 by andypost, alexpott, daffie: Improve hash() calculation for PHP 8.1

core/modules/aggregator/src/ItemsImporter.php

@@ -108,7 +108,7 @@ public function refresh(FeedInterface $feed) {
     // We store the hash of feed data in the database. When refreshing a
     // feed we compare stored hash and new hash calculated from downloaded
     // data. If both are equal we say that feed is not updated.
-    $hash = hash('sha256', $feed->source_string);
+    $hash = $success ? hash('sha256', $feed->source_string) : '';
     $has_new_content = $success && ($feed->getHash() != $hash);
 
     if ($has_new_content) {