BUGFIX: Allow null to be returned from getFullElasticSearchHitForNode()

As the comment says, this might return `null`

Author: kdambekalns

Classes/Eel/ElasticSearchQueryBuilder.php

@@ -558,7 +558,7 @@ public function getFrom(): int
      * @param NodeInterface $node
      * @return array the Elasticsearch hit for the node as array, or NULL if it does not exist.
      */
-    public function getFullElasticSearchHitForNode(NodeInterface $node): array
+    public function getFullElasticSearchHitForNode(NodeInterface $node): ?array
     {
         return $this->elasticSearchHitsIndexedByNodeFromLastRequest[$node->getIdentifier()] ?? null;
     }