In an ODL 3 node cluster setup, when the following operations were performed we have seen couple of NPEs in the logs and observed that sometimes ping to FIP is failing.

Steps executed:
---------------
Start a VM, add FIP, kill compute on which the VM is running, delete the vm, create a new VM, attach the FIP to the VM.

2018-06-19T12:38:37,477 | ERROR | org.opendaylight.yang.gen.v1.urn.huawei.params.xml.ns.yang.l3vpn.rev140815.vpn.instances.VpnInstance_AsyncDataTreeChangeListenerBase-DataTreeChangeHandler-1 | AsyncDataTreeChangeListenerBase | 259 - org.opendaylight.genius.mdsalutil-api - 0.4.0.redhat-10 | Thread terminated due to uncaught exception: org.opendaylight.yang.gen.v1.urn.huawei.params.xml.ns.yang.l3vpn.rev140815.vpn.instances.VpnInstance_AsyncDataTreeChangeListenerBase-DataTreeChangeHandler-1
java.lang.NullPointerException: null
at org.opendaylight.netvirt.vpnmanager.VpnInterfaceManager.lambda$updateVpnInterfacesForUnProcessAdjancencies$20(VpnInterfaceManager.java:2129) ~[?:?]
at java.util.ArrayList.forEach(ArrayList.java:1257) [?:?]
at org.opendaylight.netvirt.vpnmanager.VpnInterfaceManager.updateVpnInterfacesForUnProcessAdjancencies(VpnInterfaceManager.java:2129) [366:org.opendaylight.netvirt.vpnmanager-impl:0.6.0.redhat-10]
at org.opendaylight.netvirt.vpnmanager.VpnInstanceListener.update(VpnInstanceListener.java:150) [366:org.opendaylight.netvirt.vpnmanager-impl:0.6.0.redhat-10]
at org.opendaylight.netvirt.vpnmanager.VpnInstanceListener.update(VpnInstanceListener.java:65) [366:org.opendaylight.netvirt.vpnmanager-impl:0.6.0.redhat-10]
at org.opendaylight.genius.datastoreutils.AsyncDataTreeChangeListenerBase$DataTreeChangeHandler.run(AsyncDataTreeChangeListenerBase.java:172) [259:org.opendaylight.genius.mdsalutil-api:0.4.0.redhat-10]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:?]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:?]
at java.lang.Thread.run(Thread.java:748) [?:?]