minor improve

Author: VGalaxies

iotdb-client/session/src/main/java/org/apache/iotdb/session/subscription/consumer/base/AbstractSubscriptionConsumer.java

@@ -975,13 +975,10 @@ private Optional<SubscriptionMessage> pollTabletsInternal(
       final List<SubscriptionPollResponse> responses =
           pollTabletsInternal(commitContext, nextOffset, timer.remainingMs());
 
-      // It's agreed that the server will always return at least one response, even in case of
-      // failure.
+      // If responses is empty, it means that some outdated subscription events may be being polled,
+      // so just return.
       if (responses.isEmpty()) {
-        final String errorMessage =
-            String.format("SubscriptionConsumer %s poll empty response", this);
-        LOGGER.warn(errorMessage);
-        throw new SubscriptionRuntimeNonCriticalException(errorMessage);
+        return Optional.empty();
       }
 
       // only one SubscriptionEvent polled currently