ODL controller catch exception about onTransactionChainFailed when BGP neighbor was down.

opendaylight-user@root>Exception in thread "CommitFutures-192" java.lang.NullPointerException
at org.opendaylight.protocol.bgp.rib.impl.RIBImpl.onTransactionChainFailed(RIBImpl.java:248)
at org.opendaylight.controller.md.sal.dom.broker.impl.PingPongTransactionChain$1.onTransactionChainFailed(PingPongTransactionChain.java:102)
at org.opendaylight.controller.cluster.databroker.DOMBrokerTransactionChain.transactionFailed(DOMBrokerTransactionChain.java:137)
at org.opendaylight.controller.cluster.databroker.DOMBrokerTransactionChain.access$100(DOMBrokerTransactionChain.java:30)
at org.opendaylight.controller.cluster.databroker.DOMBrokerTransactionChain$1.onFailure(DOMBrokerTransactionChain.java:98)
at com.google.common.util.concurrent.Futures$6.run(Futures.java:1310)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)
Exception in thread "CommitFutures-193" java.lang.IllegalStateException: Attempted to close chain with outstanding transaction PingPongTransaction

{delegate=org.opendaylight.controller.cluster.databroker.DOMBrokerReadWriteTransaction@463807c}

at com.google.common.base.Preconditions.checkState(Preconditions.java:197)
at org.opendaylight.controller.md.sal.dom.broker.impl.PingPongTransactionChain.close(PingPongTransactionChain.java:259)
at org.opendaylight.protocol.bgp.rib.impl.BGPPeer.onTransactionChainFailed(BGPPeer.java:321)
at org.opendaylight.controller.md.sal.dom.broker.impl.PingPongTransactionChain$1.onTransactionChainFailed(PingPongTransactionChain.java:102)
at org.opendaylight.controller.cluster.databroker.DOMBrokerTransactionChain.transactionFailed(DOMBrokerTransactionChain.java:137)
at org.opendaylight.controller.cluster.databroker.DOMBrokerTransactionChain.access$100(DOMBrokerTransactionChain.java:30)
at org.opendaylight.controller.cluster.databroker.DOMBrokerTransactionChain$1.onFailure(DOMBrokerTransactionChain.java:98)
at com.google.common.util.concurrent.Futures$6.run(Futures.java:1310)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:744)