Fix warning handler used in DataStreamsUpgradeIT (#59960)

qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/IndexingIT.java

@@ -43,6 +43,8 @@ import static org.hamcrest.Matchers.either;
  * duplication but for now we have no real way to share code.
  */
 public class IndexingIT extends AbstractRollingTestCase {
+
+    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/59935")
     public void testIndexing() throws IOException {
         switch (CLUSTER_TYPE) {
         case OLD:

test/framework/src/main/java/org/elasticsearch/test/rest/ESRestTestCase.java

@@ -1435,8 +1435,15 @@ public abstract class ESRestTestCase extends ESTestCase {
     protected static void useIgnoreMultipleMatchingTemplatesWarningsHandler(Request request) throws IOException {
         RequestOptions.Builder options = request.getOptions().toBuilder();
         options.setWarningsHandler(warnings -> {
-            return warnings.stream().anyMatch(message -> CREATE_INDEX_MULTIPLE_MATCHING_TEMPLATES.matcher(message).matches() ||
-                PUT_TEMPLATE_MULTIPLE_MATCHING_TEMPLATES.matcher(message).matches());
+            if (warnings.size() > 0) {
+                boolean matches = warnings.stream().anyMatch(
+                    message -> CREATE_INDEX_MULTIPLE_MATCHING_TEMPLATES.matcher(message).matches() ||
+                    PUT_TEMPLATE_MULTIPLE_MATCHING_TEMPLATES.matcher(message).matches());
+                return matches == false;
+            } else {
+                return false;
+            }
         });
+        request.setOptions(options);
     }
 }