check curator event with empty data value (#4126)

fixes #3866

Author: cvictory

dubbo-remoting/dubbo-remoting-zookeeper/src/main/java/org/apache/dubbo/remoting/zookeeper/curator/CuratorZookeeperClient.java

@@ -17,6 +17,8 @@
 package org.apache.dubbo.remoting.zookeeper.curator;
 
 import org.apache.dubbo.common.URL;
+import org.apache.dubbo.common.logger.Logger;
+import org.apache.dubbo.common.logger.LoggerFactory;
 import org.apache.dubbo.common.utils.StringUtils;
 import org.apache.dubbo.remoting.zookeeper.ChildListener;
 import org.apache.dubbo.remoting.zookeeper.DataListener;
@@ -49,6 +51,8 @@
 
 public class CuratorZookeeperClient extends AbstractZookeeperClient<CuratorZookeeperClient.CuratorWatcherImpl, CuratorZookeeperClient.CuratorWatcherImpl> {
 
+    protected static final Logger logger = LoggerFactory.getLogger(CuratorZookeeperClient.class);
+
     static final Charset CHARSET = Charset.forName("UTF-8");
     private final CuratorFramework client;
     private Map<String, TreeCache> treeCacheMap = new ConcurrentHashMap<>();
@@ -288,6 +292,9 @@ public void process(WatchedEvent event) throws Exception {
         @Override
         public void childEvent(CuratorFramework client, TreeCacheEvent event) throws Exception {
             if (dataListener != null) {
+                if (logger.isInfoEnabled()) {
+                    logger.info("listen the zookeeper changed. The changed data:" + event.getData());
+                }
                 TreeCacheEvent.Type type = event.getType();
                 EventType eventType = null;
                 String content = null;
@@ -296,12 +303,12 @@ public void childEvent(CuratorFramework client, TreeCacheEvent event) throws Exc
                     case NODE_ADDED:
                         eventType = EventType.NodeCreated;
                         path = event.getData().getPath();
-                        content = new String(event.getData().getData(), CHARSET);
+                        content = event.getData().getData() == null ? "" : new String(event.getData().getData(), CHARSET);
                         break;
                     case NODE_UPDATED:
                         eventType = EventType.NodeDataChanged;
                         path = event.getData().getPath();
-                        content = new String(event.getData().getData(), CHARSET);
+                        content = event.getData().getData() == null ? "" : new String(event.getData().getData(), CHARSET);
                         break;
                     case NODE_REMOVED:
                         path = event.getData().getPath();