NPE in ComputerListener#onConfigurationChange breaks Jenkins

java.lang.NullPointerException
	at smartjenkins.SmartJenkinsComputerListener.onConfigurationChange(SmartJenkinsComputerListener.java:41)
	at hudson.model.AbstractCIBase.updateComputerList(AbstractCIBase.java:231)
	at jenkins.model.Jenkins.updateComputerList(Jenkins.java:1547)
	at jenkins.model.Nodes$8.run(Nodes.java:333)
	at hudson.model.Queue._withLock(Queue.java:1375)
	at hudson.model.Queue.withLock(Queue.java:1252)
	at jenkins.model.Nodes.load(Nodes.java:324)
	at jenkins.model.Jenkins$14.run(Jenkins.java:3060)
	at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:169)
	at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:296)
	at jenkins.model.Jenkins$5.runTask(Jenkins.java:1064)
	at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:214)
	at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:117)
	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)
Caused: org.jvnet.hudson.reactor.ReactorException
	at org.jvnet.hudson.reactor.Reactor.execute(Reactor.java:282)
	at jenkins.InitReactorRunner.run(InitReactorRunner.java:48)
	at jenkins.model.Jenkins.executeReactor(Jenkins.java:1098)
	at jenkins.model.Jenkins.<init>(Jenkins.java:900)
	at hudson.model.Hudson.<init>(Hudson.java:85)
	at hudson.model.Hudson.<init>(Hudson.java:81)
	at hudson.WebAppMain$3.run(WebAppMain.java:233)
Caused: hudson.util.HudsonFailedToLoad
	at hudson.WebAppMain$3.run(WebAppMain.java:250)