NullPointerException when redo Command is passed negative value

When negative value of argument is passed to redo command .

[zk: localhost:2181(CONNECTED) 0] redo -1
Exception in thread "main" java.lang.NullPointerException
at java.util.StringTokenizer.<init>(Unknown Source)
at java.util.StringTokenizer.<init>(Unknown Source)
at org.apache.zookeeper.ZooKeeperMain$MyCommandOptions.parseCommand(ZooKeeperMain.java:227)
at org.apache.zookeeper.ZooKeeperMain.processZKCmd(ZooKeeperMain.java:645)
at org.apache.zookeeper.ZooKeeperMain.processCmd(ZooKeeperMain.java:588)
at org.apache.zookeeper.ZooKeeperMain.executeLine(ZooKeeperMain.java:360)
at org.apache.zookeeper.ZooKeeperMain.run(ZooKeeperMain.java:323)
at org.apache.zookeeper.ZooKeeperMain.main(ZooKeeperMain.java:282)