diff --git a/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/protocol/mqtt/MPPPublishHandler.java b/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/protocol/mqtt/MPPPublishHandler.java
index 86dc21631e6b9..9f10400759107 100644
--- a/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/protocol/mqtt/MPPPublishHandler.java
+++ b/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/protocol/mqtt/MPPPublishHandler.java
@@ -91,6 +91,10 @@ public String getID() {
 
   @Override
   public void onConnect(InterceptConnectMessage msg) {
+    if (msg.getClientID() == null || msg.getClientID().trim().isEmpty()) {
+      LOG.error(
+          "Connection refused: client_id is missing or empty. A valid client_id is required to establish a connection.");
+    }
     if (!clientIdToSessionMap.containsKey(msg.getClientID())) {
       MqttClientSession session = new MqttClientSession(msg.getClientID());
       sessionManager.login(
diff --git a/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/execution/config/executor/ClusterConfigTaskExecutor.java b/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/execution/config/executor/ClusterConfigTaskExecutor.java
index d1a668a5888eb..86e42530e113b 100644
--- a/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/execution/config/executor/ClusterConfigTaskExecutor.java
+++ b/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/execution/config/executor/ClusterConfigTaskExecutor.java
@@ -3650,8 +3650,10 @@ public SettableFuture<ConfigTaskResult> dropDatabase(
   }
 
   public static void unsetDatabaseIfNotExist(final String database, final IClientSession session) {
-    if (database.equals(session.getDatabaseName())) {
-      session.setDatabaseName(null);
+    if (session != null) {
+      if (database.equals(session.getDatabaseName())) {
+        session.setDatabaseName(null);
+      }
     }
   }
 
diff --git a/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/service/MQTTService.java b/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/service/MQTTService.java
index 08d8fe71b8fa5..c6cc3fa47ee10 100644
--- a/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/service/MQTTService.java
+++ b/iotdb-core/datanode/src/main/java/org/apache/iotdb/db/service/MQTTService.java
@@ -96,7 +96,7 @@ private IConfig createBrokerConfig(IoTDBConfig iotDBConfig) {
         BrokerConstants.DATA_PATH_PROPERTY_NAME, String.valueOf(iotDBConfig.getMqttDataPath()));
     properties.setProperty(BrokerConstants.IMMEDIATE_BUFFER_FLUSH_PROPERTY_NAME, "true");
     properties.setProperty(BrokerConstants.ALLOW_ANONYMOUS_PROPERTY_NAME, "false");
-    properties.setProperty(BrokerConstants.ALLOW_ZERO_BYTE_CLIENT_ID_PROPERTY_NAME, "true");
+    properties.setProperty(BrokerConstants.ALLOW_ZERO_BYTE_CLIENT_ID_PROPERTY_NAME, "false");
     properties.setProperty(
         BrokerConstants.NETTY_MAX_BYTES_PROPERTY_NAME,
         String.valueOf(iotDBConfig.getMqttMaxMessageSize()));