Reactive Forwarding: fixBlackhole NPE

When a host is removed (e.g. as a result of a port down), we get the following NPE (NullPointerException) when computing/fixing blackholed traffic.

hostService.getHost(HostId.hostId(sd.src)) returns null

To reproduce:
– Start a mininet network (any topology0
– Run pingall in mininet
– Quit mininet

2015-07-23 14:29:28,124 | WARN | event-dispatch-0 | ListenerRegistry | 74 - org.onosproject.onos-api - 1.3.0.SNAPSHOT | Exception encountered while processing event TopologyEvent{time=2015-07-23T14:29:28.123, type=TOPOLOGY_CHANGED, subject=DefaultTopology{time=488602853248094, creationTime=1437686968123, computeCost=342135, clusters=3, devices=4, links=2}}
java.lang.NullPointerException
at org.onosproject.fwd.ReactiveForwarding.fixBlackhole(ReactiveForwarding.java:701)[171:org.onosproject.onos-app-fwd:1.3.0.SNAPSHOT]
at org.onosproject.fwd.ReactiveForwarding.access$1000(ReactiveForwarding.java:89)[171:org.onosproject.onos-app-fwd:1.3.0.SNAPSHOT]
at org.onosproject.fwd.ReactiveForwarding$InternalTopologyListener.lambda$event$0(ReactiveForwarding.java:685)[171:org.onosproject.onos-app-fwd:1.3.0.SNAPSHOT]
at org.onosproject.fwd.ReactiveForwarding$InternalTopologyListener$$Lambda$395/181094131.accept(Unknown Source)[171:org.onosproject.onos-app-fwd:1.3.0.SNAPSHOT]
at java.util.ArrayList.forEach(ArrayList.java:1249)[:1.8.0_25]
at org.onosproject.fwd.ReactiveForwarding$InternalTopologyListener.event(ReactiveForwarding.java:681)[171:org.onosproject.onos-app-fwd:1.3.0.SNAPSHOT]
at org.onosproject.fwd.ReactiveForwarding$InternalTopologyListener.event(ReactiveForwarding.java:676)[171:org.onosproject.onos-app-fwd:1.3.0.SNAPSHOT]
at org.onosproject.event.ListenerRegistry.process(ListenerRegistry.java:75)[74:org.onosproject.onos-api:1.3.0.SNAPSHOT]
at org.onosproject.event.impl.CoreEventDispatcher$DispatchLoop.process(CoreEventDispatcher.java:139)[76:org.onosproject.onos-core-net:1.3.0.SNAPSHOT]
at org.onosproject.event.impl.CoreEventDispatcher$DispatchLoop.run(CoreEventDispatcher.java:124)[76:org.onosproject.onos-core-net:1.3.0.SNAPSHOT]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)[:1.8.0_25]
at java.util.concurrent.FutureTask.run(FutureTask.java:266)[:1.8.0_25]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)[:1.8.0_25]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)[:1.8.0_25]
at java.lang.Thread.run(Thread.java:745)[:1.8.0_25]