Inventory does not clear after switch disconnects

To reproduce:

• Start mininet 1 switch sudo mn --controller 'remote,ip=127.0.0.1,port=6633' --topo tree,1
• Stop mininet and check inventory.
• Repeat a few times if the issue does not show the first time.

This exception is also seen in karaf log:

2015-11-18 08:54:59,179 | WARN | entLoopGroup-6-3 | ConnectionConductorImpl | 194 - org.opendaylight.openflowplugin - 0.1.3.SNAPSHOT | Failed to close queueKeeper
java.lang.NullPointerException: pollRegistration not available
at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:226)[64:com.google.guava:18.0.0]
at org.opendaylight.openflowplugin.openflow.md.queue.QueueKeeperFairImpl.close(QueueKeeperFairImpl.java:43)[194:org.opendaylight.openflowplugin:0.1.3.SNAPSHOT]
at org.opendaylight.openflowplugin.openflow.md.core.ConnectionConductorImpl.onDisconnectEvent(ConnectionConductorImpl.java:408)[194:org.opendaylight.openflowplugin:0.1.3.SNAPSHOT]
at org.opendaylight.openflowjava.protocol.impl.core.connection.ConnectionAdapterImpl.consume(ConnectionAdapterImpl.java:280)[191:org.opendaylight.openflowjava.openflow-protocol-impl:0.6.3.SNAPSHOT]
at org.opendaylight.openflowjava.protocol.impl.core.DelegatingInboundHandler.channelInactive(DelegatingInboundHandler.java:55)[191:org.opendaylight.openflowjava.openflow-protocol-impl:0.6.3.SNAPSHOT]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:237)[119:io.netty.transport:4.0.26.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:223)[119:io.netty.transport:4.0.26.Final]
at io.netty.channel.ChannelInboundHandlerAdapter.channelInactive(ChannelInboundHandlerAdapter.java:75)[119:io.netty.transport:4.0.26.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:237)[119:io.netty.transport:4.0.26.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:223)[119:io.netty.transport:4.0.26.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelInactive(ByteToMessageDecoder.java:294)[145:io.netty.codec:4.0.26.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:237)[119:io.netty.transport:4.0.26.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:223)[119:io.netty.transport:4.0.26.Final]
at io.netty.handler.codec.ByteToMessageDecoder.channelInactive(ByteToMessageDecoder.java:294)[145:io.netty.codec:4.0.26.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:237)[119:io.netty.transport:4.0.26.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:223)[119:io.netty.transport:4.0.26.Final]
at io.netty.channel.ChannelInboundHandlerAdapter.channelInactive(ChannelInboundHandlerAdapter.java:75)[119:io.netty.transport:4.0.26.Final]
at io.netty.handler.timeout.ReadTimeoutHandler.channelInactive(ReadTimeoutHandler.java:144)[146:io.netty.handler:4.0.26.Final]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:237)[119:io.netty.transport:4.0.26.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:223)[119:io.netty.transport:4.0.26.Final]
at io.netty.channel.ChannelInboundHandlerAdapter.channelInactive(ChannelInboundHandlerAdapter.java:75)[119:io.netty.transport:4.0.26.Final]
at org.opendaylight.openflowjava.protocol.impl.core.connection.ChannelOutboundQueue.channelInactive(ChannelOutboundQueue.java:256)[191:org.opendaylight.openflowjava.openflow-protocol-impl:0.6.3.SNAPSHOT]
at io.netty.channel.AbstractChannelHandlerContext.invokeChannelInactive(AbstractChannelHandlerContext.java:237)[119:io.netty.transport:4.0.26.Final]
at io.netty.channel.AbstractChannelHandlerContext.fireChannelInactive(AbstractChannelHandlerContext.java:223)[119:io.netty.transport:4.0.26.Final]
at io.netty.channel.DefaultChannelPipeline.fireChannelInactive(DefaultChannelPipeline.java:829)[119:io.netty.transport:4.0.26.Final]
at io.netty.channel.AbstractChannel$AbstractUnsafe$7.run(AbstractChannel.java:610)[119:io.netty.transport:4.0.26.Final]
at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:328)[120:io.netty.common:4.0.26.Final]
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:350)[119:io.netty.transport:4.0.26.Final]
at io.netty.util.concurrent.SingleThreadEventExecutor$2.run(SingleThreadEventExecutor.java:111)[120:io.netty.common:4.0.26.Final]
at io.netty.util.concurrent.DefaultThreadFactory$DefaultRunnableDecorator.run(DefaultThreadFactory.java:137)[120:io.netty.common:4.0.26.Final]
at java.lang.Thread.run(Thread.java:745)[:1.7.0_79]
2015-11-18 08:54:59,256 | INFO | entLoopGroup-6-4 | ConnectionAdapterImpl | 191 - org.opendaylight.openflowjava.openflow-protocol-impl