NullPointerException thrown by SwitchManager when adding nodes.

To reproduce,

1. Get the openflowplugin repo
2. mvn clean install from root
3. Got to the distribution folder and run it.
4. Once the controller has started using mininet add topology using the following command. You should see the following exception,

2014-02-19 17:39:55.274 PST [md-sal-binding-notification-0] ERROR o.o.c.sal.binding.impl.NotifyTask - Unhandled exception thrown by listener: org.opendaylight.controller.sal.compatibility.InventoryAndReadAdapter$$Broker$ListenerInvoker@7e06f25b
java.lang.NullPointerException: Null values are not supported!
at org.infinispan.CacheImpl.assertValueNotNull(CacheImpl.java:207) ~[na:na]
at org.infinispan.CacheImpl.replaceInternal(CacheImpl.java:982) ~[na:na]
at org.infinispan.CacheImpl.replace(CacheImpl.java:976) ~[na:na]
at org.infinispan.CacheImpl.replace(CacheImpl.java:1400) ~[na:na]
at org.infinispan.CacheImpl.replace(CacheImpl.java:264) ~[na:na]
at org.opendaylight.controller.switchmanager.internal.SwitchManager.addNode(SwitchManager.java:1039) ~[na:na]
at org.opendaylight.controller.switchmanager.internal.SwitchManager.updateNode(SwitchManager.java:1137) ~[na:na]
at org.opendaylight.controller.sal.implementation.internal.Inventory.updateNode(Inventory.java:115) ~[na:na]
at org.opendaylight.controller.sal.compatibility.InventoryAndReadAdapter.publishNodeUpdate(InventoryAndReadAdapter.java:1031) ~[na:na]
at org.opendaylight.controller.sal.compatibility.InventoryAndReadAdapter.onNodeUpdated(InventoryAndReadAdapter.java:631) ~[na:na]
at org.opendaylight.controller.sal.compatibility.InventoryAndReadAdapter$$Broker$ListenerInvoker.onNotification(InventoryAndReadAdapter$$Broker$ListenerInvoker.java) ~[na:na]
at org.opendaylight.controller.sal.binding.impl.NotifyTask.call(NotifyTask.java:59) ~[na:na]
at java.util.concurrent.FutureTask.run(FutureTask.java:262) [na:1.7.0_45]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145) [na:1.7.0_45]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615) [na:1.7.0_45]
at java.lang.Thread.run(Thread.java:744) [na:1.7.0_45]