NPE when executors are down but events are still coming in

Minor annoyance when shutting down a cluster and the master is still receiving events from Zookeeper:

2011-09-22 23:53:01,552 DEBUG org.apache.hadoop.hbase.zookeeper.ZooKeeperWatcher: master:60000-0x3292d87deb004f Received InterruptedException, doing nothing here
java.lang.InterruptedException
at java.lang.Object.wait(Native Method)
at java.lang.Object.wait(Object.java:485)
at org.apache.zookeeper.ClientCnxn.submitRequest(ClientCnxn.java:1317)
at org.apache.zookeeper.ZooKeeper.delete(ZooKeeper.java:726)
at org.apache.hadoop.hbase.zookeeper.ZKUtil.deleteNode(ZKUtil.java:938)
at org.apache.hadoop.hbase.zookeeper.ZKAssign.deleteNode(ZKAssign.java:407)
at org.apache.hadoop.hbase.zookeeper.ZKAssign.deleteOpenedNode(ZKAssign.java:284)
at org.apache.hadoop.hbase.master.handler.OpenedRegionHandler.process(OpenedRegionHandler.java:88)
at org.apache.hadoop.hbase.executor.EventHandler.run(EventHandler.java:156)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
...
2011-09-22 23:53:01,558 DEBUG org.apache.hadoop.hbase.executor.ExecutorService: Executor service [MASTER_OPEN_REGION-sv2borg170:60000] not found in {}
2011-09-22 23:53:01,558 ERROR org.apache.zookeeper.ClientCnxn: Error while calling watcher
java.lang.NullPointerException
at org.apache.hadoop.hbase.executor.ExecutorService.submit(ExecutorService.java:220)
at org.apache.hadoop.hbase.master.AssignmentManager.handleRegion(AssignmentManager.java:447)
at org.apache.hadoop.hbase.master.AssignmentManager.nodeDataChanged(AssignmentManager.java:546)
at org.apache.hadoop.hbase.zookeeper.ZooKeeperWatcher.process(ZooKeeperWatcher.java:281)
at org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:530)
at org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:506)

It's annoying because it then spams you with a bunch of NPEs that have nothing to do with the reason the Master is shutting down. Googling I saw someone also had that issue in June: http://pastebin.com/5Tqrj0nq