Update log for null item to warn

Signed-off-by: Brendan Benner <bbenner@amazon.com>

Author: Brendan Benner

data-prepper-plugins/saas-source-plugins/source-crawler/src/main/java/org/opensearch/dataprepper/plugins/source/source_crawler/base/TokenPaginationCrawler.java

@@ -64,7 +64,7 @@ public Instant crawl(LeaderPartition leaderPartition,
                 final ItemInfo nextItem = itemInfoIterator.next();
                 if (nextItem == null) {
                     //we don't expect null items, but just in case, we'll skip them
-                    log.info("Unexpected encounter of a null item.");
+                    log.warn("Unexpected encounter of a null item while processing batch with last item ID " + lastToken);
                     invalidPaginationItemsCounter.increment();
                     continue;
                 }