Occasionally, DTCL delete notification does not include "data before"

Remote peer advertise 1M routes then it is disconnected, empty topology is expected, NPE appeared instead:

araf | command | 306 - org.apache.karaf.log.command - 3.0.7 | ROBOT MESSAGE: Starting test Kill_Talking_BGP_Speaker
2016-08-30 02:41:19,795 | INFO | entLoopGroup-5-1 | BGPSessionImpl | 185 - org.opendaylight.bgpcep.bgp-rib-impl - 0.6.0.SNAPSHOT | End of input detected. Close the session.
2016-08-30 02:41:19,795 | INFO | entLoopGroup-5-1 | BGPPeer | 185 - org.opendaylight.bgpcep.bgp-rib-impl - 0.6.0.SNAPSHOT | Session with peer 10.29.12.104 went down
2016-08-30 02:41:19,809 | INFO | entLoopGroup-5-1 | BGPSessionImpl | 185 - org.opendaylight.bgpcep.bgp-rib-impl - 0.6.0.SNAPSHOT | Closing session: BGPSessionImpl

{channel=[id: 0x45b8e831, L:/10.29.13.40:1790 ! R:/10.29.12.104:17900], state=UP}

2016-08-30 02:41:19,919 | INFO | h for user karaf | command | 306 - org.apache.karaf.log.command - 3.0.7 | ROBOT MESSAGE: Starting test Store_Results_For_Talking_BGP_Speaker
2016-08-30 02:41:20,375 | INFO | h for user karaf | command | 306 - org.apache.karaf.log.command - 3.0.7 | ROBOT MESSAGE: Starting test Wait_For_Stable_Ipv4_Topology_After_Talking
2016-08-30 02:41:28,659 | WARN | on-dispatcher-46 | AbstractTopologyBuilder | 191 - org.opendaylight.bgpcep.bgp-topology-provider - 0.6.0.SNAPSHOT | Data change LazyDataTreeModification{path = DataTreeIdentifier{datastoreType = OPERATIONAL, rootIdentifier = KeyedInstanceIdentifier{targetType=interface org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.inet.rev150305.ipv4.routes.ipv4.routes.Ipv4Route, path=[org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.rib.rev130925.BgpRib, org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.rib.rev130925.bgp.rib.Rib[key=RibKey [_id=Uri [_value=example-bgp-rib]]], org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.rib.rev130925.bgp.rib.rib.LocRib, org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.rib.rev130925.rib.Tables[key=TablesKey [_afi=class org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.types.rev130919.Ipv4AddressFamily, _safi=class org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.types.rev130919.UnicastSubsequentAddressFamily]], org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.inet.rev150305.ipv4.routes.Ipv4Routes, org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.inet.rev150305.ipv4.routes.ipv4.routes.Ipv4Route[key=Ipv4RouteKey [_prefix=Ipv4Prefix [_value=9.84.88.112/28], _pathId=PathId [_value=0]]]]}}, rootNode = LazyDataObjectModification{identifier = org.opendaylight.yang.gen.v1.urn.opendaylight.params.xml.ns.yang.bgp.inet.rev150305.ipv4.routes.ipv4.routes.Ipv4Route[key=Ipv4RouteKey [_prefix=Ipv4Prefix [_value=9.84.88.112/28], _pathId=PathId [_value=0]]], domData = ChildNode{mod = NodeModification [identifier=(urn:opendaylight:params:xml:ns:yang:bgp-inet?revision=2015-03-05)ipv4-route[

{(urn:opendaylight:params:xml:ns:yang:bgp-inet?revision=2015-03-05)path-id=0, (urn:opendaylight:params:xml:ns:yang:bgp-inet?revision=2015-03-05)prefix=9.84.88.112/28}

], modificationType=DELETE, childModification={}], oldMeta = null, newMeta = null}}} (transaction DOM-CHAIN-4-364481) was not completely propagated to listener org.opendaylight.bgpcep.bgp.topology.provider.Ipv4ReachabilityTopologyBuilder@245a6da5
java.lang.NullPointerException
at org.opendaylight.bgpcep.bgp.topology.provider.Ipv4ReachabilityTopologyBuilder.getAttributes(Ipv4ReachabilityTopologyBuilder.java:41)[191:org.opendaylight.bgpcep.bgp-topology-provider:0.6.0.SNAPSHOT]
at org.opendaylight.bgpcep.bgp.topology.provider.Ipv4ReachabilityTopologyBuilder.getAttributes(Ipv4ReachabilityTopologyBuilder.java:27)[191:org.opendaylight.bgpcep.bgp-topology-provider:0.6.0.SNAPSHOT]
at org.opendaylight.bgpcep.bgp.topology.provider.AbstractReachabilityTopologyBuilder.removeObject(AbstractReachabilityTopologyBuilder.java:145)[191:org.opendaylight.bgpcep.bgp-topology-provider:0.6.0.SNAPSHOT]
at org.opendaylight.bgpcep.bgp.topology.provider.AbstractTopologyBuilder.routeChanged(AbstractTopologyBuilder.java:213)[191:org.opendaylight.bgpcep.bgp-topology-provider:0.6.0.SNAPSHOT]
at org.opendaylight.bgpcep.bgp.topology.provider.AbstractTopologyBuilder.onDataTreeChanged(AbstractTopologyBuilder.java:175)[191:org.opendaylight.bgpcep.bgp-topology-provider:0.6.0.SNAPSHOT]
at org.opendaylight.controller.md.sal.binding.impl.BindingDOMDataTreeChangeListenerAdapter.onDataTreeChanged(BindingDOMDataTreeChangeListenerAdapter.java:41)[143:org.opendaylight.controller.sal-binding-broker-impl:1.4.0.SNAPSHOT]
at org.opendaylight.controller.cluster.datastore.DataTreeChangeListenerActor.dataChanged(DataTreeChangeListenerActor.java:55)[172:org.opendaylight.controller.sal-distributed-datastore:1.4.0.SNAPSHOT]
at org.opendaylight.controller.cluster.datastore.DataTreeChangeListenerActor.handleReceive(DataTreeChangeListenerActor.java:37)[172:org.opendaylight.controller.sal-distributed-datastore:1.4.0.SNAPSHOT]
at org.opendaylight.controller.cluster.common.actor.AbstractUntypedActor.onReceive(AbstractUntypedActor.java:26)[167:org.opendaylight.controller.sal-clustering-commons:1.4.0.SNAPSHOT]
at akka.actor.UntypedActor$$anonfun$receive$1.applyOrElse(UntypedActor.scala:165)[155:com.typesafe.akka.actor:2.4.7]
at akka.actor.Actor$class.aroundReceive(Actor.scala:484)[155:com.typesafe.akka.actor:2.4.7]
at akka.actor.UntypedActor.aroundReceive(UntypedActor.scala:95)[155:com.typesafe.akka.actor:2.4.7]
at akka.actor.ActorCell.receiveMessage(ActorCell.scala:526)[155:com.typesafe.akka.actor:2.4.7]
at akka.actor.ActorCell.invoke(ActorCell.scala:495)[155:com.typesafe.akka.actor:2.4.7]
at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:257)[155:com.typesafe.akka.actor:2.4.7]
at akka.dispatch.Mailbox.run(Mailbox.scala:224)[155:com.typesafe.akka.actor:2.4.7]
at akka.dispatch.Mailbox.exec(Mailbox.scala:234)[155:com.typesafe.akka.actor:2.4.7]
at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)[151:org.scala-lang.scala-library:2.11.8.v20160304-115712-1706a37eb8]
at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)[151:org.scala-lang.scala-library:2.11.8.v20160304-115712-1706a37eb8]
at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)[151:org.scala-lang.scala-library:2.11.8.v20160304-115712-1706a37eb8]
at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)[151:org.scala-lang.scala-library:2.11.8.v20160304-115712-1706a37eb8]