a group has two nodes, lots of threads in the two nodes will compete locks (same lock name)
it's a intermittent issue, only meet twice in 12 hours longivity test.

below is the exception:

2012-05-17 01:41:20,232 ERROR [org.jgroups.protocols.UNICAST][Incoming-2,7fffffff-848a-e17f-7fff-ffffffd0d52f_domainservice,PEK-WKST1DBTB-7271] couldn't deliver message [dst: PEK-WKST1DBTB-7271, src: pek-wkstdkktk-44853 (3 headers), size=81 bytes, flags=DONT_BUNDLE]
java.lang.NullPointerException
at org.jgroups.blocks.locking.Owner.equals(Owner.java:50)
at org.jgroups.protocols.Locking$ServerLock.handleRequest(Locking.java:689)
at org.jgroups.protocols.Locking.handleLockRequest(Locking.java:433)
at org.jgroups.protocols.Locking.up(Locking.java:231)
at org.jgroups.protocols.pbcast.STATE_TRANSFER.up(STATE_TRANSFER.java:150)
at org.jgroups.protocols.FRAG2.up(FRAG2.java:189)
at org.jgroups.protocols.FlowControl.up(FlowControl.java:418)
at org.jgroups.protocols.FlowControl.up(FlowControl.java:400)
at org.jgroups.protocols.pbcast.GMS.up(GMS.java:891)
at org.jgroups.protocols.pbcast.STABLE.up(STABLE.java:246)
at org.jgroups.protocols.VIEW_SYNC.up(VIEW_SYNC.java:170)
at org.jgroups.protocols.UNICAST.handleDataReceived(UNICAST.java:613)
at org.jgroups.protocols.UNICAST.up(UNICAST.java:294)
at org.jgroups.protocols.pbcast.NAKACK.up(NAKACK.java:703)
at org.jgroups.protocols.BARRIER.up(BARRIER.java:119)
at org.jgroups.protocols.VERIFY_SUSPECT.up(VERIFY_SUSPECT.java:133)
at org.jgroups.protocols.FD_ALL.up(FD_ALL.java:177)
at org.jgroups.protocols.FD.up(FD.java:275)
at org.jgroups.protocols.FD_SOCK.up(FD_SOCK.java:275)
at org.jgroups.protocols.MERGE2.up(MERGE2.java:209)
at org.jgroups.protocols.Discovery.up(Discovery.java:293)
at org.jgroups.protocols.PING.up(PING.java:69)
at org.jgroups.protocols.MPING.up(MPING.java:176)
at org.jgroups.protocols.TP.passMessageUp(TP.java:1109)
at org.jgroups.protocols.TP$IncomingPacket.handleMyMessage(TP.java:1665)
at org.jgroups.protocols.TP$IncomingPacket.run(TP.java:1647)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)