Periodic NullPointerException with DHCP app

I got NullPointerException periodically with DHCP app, and the switch is disconnected and connected back at the same time. I didn't add any subnet to the network config. If I add some subnet (I don't use), it disappears.

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2015-11-12 04:02:41,658 | ERROR | ew I/O worker #5 | OFChannelHandler | 174 - org.onosproject.onos-of-ctl - 1.4.0.SNAPSHOT | Error while processing message from switch org.onosproject.driver.handshaker.NiciraSwitchHandshaker [/192.241.229.42:38952 DPID[00:00:00:00:00:00:00:02]]state ACTIVE
java.lang.NullPointerException
at org.onosproject.dhcp.impl.DistributedDhcpStore.ipWithinRange(DistributedDhcpStore.java:349)
at org.onosproject.dhcp.impl.DistributedDhcpStore.assignIP(DistributedDhcpStore.java:175)
at org.onosproject.dhcp.impl.DhcpManager$DHCPPacketProcessor.processDHCPPacket(DhcpManager.java:519)
at org.onosproject.dhcp.impl.DhcpManager$DHCPPacketProcessor.process(DhcpManager.java:608)
at org.onosproject.net.packet.impl.PacketManager$InternalPacketProviderService.processPacket(PacketManager.java:316)
at org.onosproject.provider.of.packet.impl.OpenFlowPacketProvider$InternalPacketProvider.handlePacket(OpenFlowPacketProvider.java:170)
at org.onosproject.openflow.controller.impl.OpenFlowControllerImpl.processPacket(OpenFlowControllerImpl.java:259)
at org.onosproject.openflow.controller.impl.OpenFlowControllerImpl$OpenFlowSwitchAgent.processMessage(OpenFlowControllerImpl.java:603)
at org.onosproject.openflow.controller.driver.AbstractOpenFlowSwitch.handleMessage(AbstractOpenFlowSwitch.java:210)
at org.onosproject.openflow.controller.impl.OFChannelHandler.dispatchMessage(OFChannelHandler.java:1185)
at org.onosproject.openflow.controller.impl.OFChannelHandler.access$1800(OFChannelHandler.java:81)
at org.onosproject.openflow.controller.impl.OFChannelHandler$ChannelState$8.processOFPacketIn(OFChannelHandler.java:636)
at org.onosproject.openflow.controller.impl.OFChannelHandler$ChannelState.processOFMessage(OFChannelHandler.java:883)
at org.onosproject.openflow.controller.impl.OFChannelHandler.messageReceived(OFChannelHandler.java:1166)
at org.jboss.netty.handler.timeout.IdleStateAwareChannelHandler.handleUpstream(IdleStateAwareChannelHandler.java:36)[45:org.jboss.netty:3.9.2.Final]
at org.jboss.netty.handler.timeout.ReadTimeoutHandler.messageReceived(ReadTimeoutHandler.java:184)[45:org.jboss.netty:3.9.2.Final]
at org.jboss.netty.handler.timeout.IdleStateHandler.messageReceived(IdleStateHandler.java:294)[45:org.jboss.netty:3.9.2.Final]
at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:296)[45:org.jboss.netty:3.9.2.Final]
at org.jboss.netty.handler.codec.frame.FrameDecoder.unfoldAndFireMessageReceived(FrameDecoder.java:462)[45:org.jboss.netty:3.9.2.Final]
at org.jboss.netty.handler.codec.frame.FrameDecoder.callDecode(FrameDecoder.java:443)[45:org.jboss.netty:3.9.2.Final]
at org.jboss.netty.handler.codec.frame.FrameDecoder.messageReceived(FrameDecoder.java:303)[45:org.jboss.netty:3.9.2.Final]
at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:268)[45:org.jboss.netty:3.9.2.Final]
at org.jboss.netty.channel.Channels.fireMessageReceived(Channels.java:255)[45:org.jboss.netty:3.9.2.Final]
at org.jboss.netty.channel.socket.nio.NioWorker.read(NioWorker.java:88)[45:org.jboss.netty:3.9.2.Final]
at org.jboss.netty.channel.socket.nio.AbstractNioWorker.process(AbstractNioWorker.java:108)[45:org.jboss.netty:3.9.2.Final]
at org.jboss.netty.channel.socket.nio.AbstractNioSelector.run(AbstractNioSelector.java:318)
at org.jboss.netty.channel.socket.nio.AbstractNioWorker.run(AbstractNioWorker.java:89)[45:org.jboss.netty:3.9.2.Final]
at org.jboss.netty.channel.socket.nio.NioWorker.run(NioWorker.java:178)[45:org.jboss.netty:3.9.2.Final]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)[:1.8.0_60]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)[:1.8.0_60]
at java.lang.Thread.run(Thread.java:745)[:1.8.0_60]
2015-11-12 04:02:41,679 | INFO | ew I/O worker #5 | OFChannelHandler | 174 - org.onosproject.onos-of-ctl - 1.4.0.SNAPSHOT | Switch disconnected callback for sw:org.onosproject.driver.handshaker.NiciraSwitchHandshaker [/192.241.229.42:38952 DPID[00:00:00:00:00:00:00:02]]. Cleaning up ...
2015-11-12 04:02:41,679 | INFO | ew I/O worker #5 | OFChannelHandler | 174 - org.onosproject.onos-of-ctl - 1.4.0.SNAPSHOT | org.onosproject.driver.handshaker.NiciraSwitchHandshaker [/192.241.229.42:38952 DPID[00:00:00:00:00:00:00:02]]:removal called
2015-11-12 04:02:41,679 | INFO | ew I/O worker #5 | DeviceManager | 143 - org.onosproject.onos-core-net - 1.4.0.SNAPSHOT | Device of:0000000000000002 disconnected from this node