[refactor] Use isEmpty() in TransactionalMessageServiceImpl

Claude Code assisted refactoring.

Signed-off-by: Senrian <senrian@github.com>

Author: Senrian

broker/src/main/java/org/apache/rocketmq/broker/transaction/queue/TransactionalMessageServiceImpl.java

@@ -164,7 +164,7 @@ public void check(long transactionTimeout, int transactionCheckMax,
         try {
             String topic = TopicValidator.RMQ_SYS_TRANS_HALF_TOPIC;
             Set<MessageQueue> msgQueues = transactionalMessageBridge.fetchMessageQueues(topic);
-            if (msgQueues == null || msgQueues.size() == 0) {
+            if (msgQueues == null || msgQueues.isEmpty()) {
                 log.warn("The queue of topic is empty :" + topic);
                 return;
             }
@@ -425,7 +425,7 @@ private PullResult fillOpRemoveMap(HashMap<Long, Long> removeMap, MessageQueue o
                 log.error("Found a illegal tag in opMessageExt= {} ", opMessageExt);
             }
 
-            if (set.size() > 0) {
+            if (!set.isEmpty()) {
                 opMsgMap.put(opMessageExt.getQueueOffset(), set);
             } else {
                 doneOpOffset.add(opMessageExt.getQueueOffset());
@@ -572,7 +572,7 @@ private GetResult getHalfMsg(MessageQueue messageQueue, long offset) {
         if (result != null) {
             getResult.setPullResult(result);
             List<MessageExt> messageExts = result.getMsgFoundList();
-            if (messageExts == null || messageExts.size() == 0) {
+            if (messageExts == null || messageExts.isEmpty()) {
                 return getResult;
             }
             getResult.setMsg(messageExts.get(0));