[IOTDB-4493] Fix null message in TSStatus (#7402)

diff --git a/confignode/src/main/java/org/apache/iotdb/confignode/manager/partition/PartitionManager.java b/confignode/src/main/java/org/apache/iotdb/confignode/manager/partition/PartitionManager.java
index 8244f38..5a81ffd 100644
--- a/confignode/src/main/java/org/apache/iotdb/confignode/manager/partition/PartitionManager.java
+++ b/confignode/src/main/java/org/apache/iotdb/confignode/manager/partition/PartitionManager.java
@@ -352,11 +352,15 @@
         result = RpcUtils.SUCCESS_STATUS;
       }
     } catch (NotEnoughDataNodeException e) {
-      LOGGER.error("ConfigNode failed to extend Region because there are not enough DataNodes");
+      String prompt = "ConfigNode failed to extend Region because there are not enough DataNodes";
+      LOGGER.error(prompt);
       result.setCode(TSStatusCode.NOT_ENOUGH_DATA_NODE.getStatusCode());
+      result.setMessage(prompt);
     } catch (StorageGroupNotExistsException e) {
-      LOGGER.error("ConfigNode failed to extend Region because some StorageGroup doesn't exist.");
+      String prompt = "ConfigNode failed to extend Region because some StorageGroup doesn't exist.";
+      LOGGER.error(prompt);
       result.setCode(TSStatusCode.STORAGE_GROUP_NOT_EXIST.getStatusCode());
+      result.setMessage(prompt);
     }
 
     return result;
diff --git a/consensus/src/main/java/org/apache/iotdb/consensus/multileader/MultiLeaderServerImpl.java b/consensus/src/main/java/org/apache/iotdb/consensus/multileader/MultiLeaderServerImpl.java
index 0488daf..1b45b3c 100644
--- a/consensus/src/main/java/org/apache/iotdb/consensus/multileader/MultiLeaderServerImpl.java
+++ b/consensus/src/main/java/org/apache/iotdb/consensus/multileader/MultiLeaderServerImpl.java
@@ -127,7 +127,9 @@
               !stateMachineCondition.await(
                   config.getReplication().getThrottleTimeOutMs(), TimeUnit.MILLISECONDS);
           if (timeout) {
-            return RpcUtils.getStatus(TSStatusCode.WRITE_PROCESS_REJECT);
+            return RpcUtils.getStatus(
+                TSStatusCode.WRITE_PROCESS_REJECT,
+                "Reject write because there are too many requests need to process");
           }
         } catch (InterruptedException e) {
           logger.error("Failed to throttle down because ", e);