Fix Hamcrest imports in S3DataSelectionIT

Author: mzurita-amz

data-prepper-plugins/s3-source/src/integrationTest/java/org/opensearch/dataprepper/plugins/source/s3/S3DataSelectionIT.java

@@ -32,6 +32,7 @@
 
 import static org.hamcrest.CoreMatchers.equalTo;
 import static org.hamcrest.CoreMatchers.notNullValue;
+import static org.hamcrest.CoreMatchers.nullValue;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.greaterThanOrEqualTo;
 import static org.mockito.ArgumentMatchers.anyCollection;
@@ -91,8 +92,8 @@ void data_and_metadata_selection_includes_both_data_and_metadata() throws Except
     void data_only_selection_includes_only_data() throws Exception {
         testS3DataSelection(S3DataSelection.DATA_ONLY, event -> {
             assertThat(event.toMap().containsKey("message"), equalTo(true)); // data content
-            assertThat(event.get("s3/bucket", String.class) == null, equalTo(true)); // no metadata
-            assertThat(event.get("s3/key", String.class) == null, equalTo(true)); // no metadata
+            assertThat(event.get("s3/bucket", String.class), nullValue()); // no metadata
+            assertThat(event.get("s3/key", String.class), nullValue()); // no metadata
         });
     }