Update PartitionBalancer.java

iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/manager/load/balancer/PartitionBalancer.java

diff --git a/iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/manager/load/balancer/PartitionBalancer.java b/iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/manager/load/balancer/PartitionBalancer.java
index 6bfa9ae..b313bc5 100644
--- a/iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/manager/load/balancer/PartitionBalancer.java
+++ b/iotdb-core/confignode/src/main/java/org/apache/iotdb/confignode/manager/load/balancer/PartitionBalancer.java
@@ -43,6 +43,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.concurrent.ConcurrentHashMap;
 
 /**
@@ -190,7 +191,7 @@
               .put(seriesPartitionEntry.getKey(), seriesPartitionTable);
         }
       } finally {
-        allotTable.releaseLock();
+        Optional.ofNullable(allotTable).ifPresent(DataPartitionPolicyTable::releaseLock);
       }
       result.put(database, dataPartitionTable);
     }