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;
                 }

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

@@ -27,6 +27,7 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.reset;
@@ -104,7 +105,7 @@ void testCrawlWithMultiplePartitions() {
     }
 
     @Test
-    void testBatchSize() {
+    void testBatchSize() {  
         List<ItemInfo> itemInfoList = new ArrayList<>();
         int maxItemsPerPage = DEFAULT_BATCH_SIZE;
         for (int i = 0; i < maxItemsPerPage; i++) {
@@ -119,7 +120,7 @@ void testBatchSize() {
         for (int i = 0; i < maxItemsPerPage * 2; i++) {
             itemInfoList2.add(new TestItemInfo("testId" + i));
         }
-        when(client.listItems(any())).thenReturn(itemInfoList2.iterator());
+        when(client.listItems(anyString())).thenReturn(itemInfoList2.iterator());
         crawler.crawl(leaderPartition, coordinator);
         expectedNumberOfInvocations += 2;
         verify(coordinator, times(expectedNumberOfInvocations)).createPartition(any(SaasSourcePartition.class));