My job stopped to poll changes from SVN some time ago - it all runs properly when started manually or by timer, but it won't poll when a change occurs in repository. I have tried tweaking with Maven installations, cloning the job etc. Other jobs using Git do not have this problem. SVN polling shows:

ERROR: Failed to record SCM polling for hudson.maven.MavenModuleSet@eafaabe[scmTest]
java.lang.IllegalArgumentException: Null value not allowed as an environment variable: M2_HOME
at hudson.EnvVars.put(EnvVars.java:172)
at hudson.tasks.Maven$MavenInstallation.buildEnvVars(Maven.java:492)
at hudson.maven.MavenModuleSetBuild.getEnvironment(MavenModuleSetBuild.java:173)
at hudson.scm.SubversionSCM.compareRemoteRevisionWith(SubversionSCM.java:1230)
at hudson.scm.SCM._compareRemoteRevisionWith(SCM.java:356)
at hudson.scm.SCM.poll(SCM.java:373)
at hudson.model.AbstractProject._poll(AbstractProject.java:1523)
at hudson.model.AbstractProject.poll(AbstractProject.java:1448)
at hudson.triggers.SCMTrigger$Runner.runPolling(SCMTrigger.java:439)
at hudson.triggers.SCMTrigger$Runner.run(SCMTrigger.java:468)
at hudson.util.SequentialExecutionQueue$QueueEntry.run(SequentialExecutionQueue.java:118)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:722)

When I get into job configuration in Maven build section I get "ERROR" below Root POM line. I am attaching the exact ERROR message as a separate file.