NPE during shutdown.
java.lang.NullPointerException
	at hudson.model.User.idStrategy(User.java:140)
	at hudson.model.User.getOrCreate(User.java:373)
	at hudson.model.User.get(User.java:366)
	at hudson.model.User.get(User.java:331)
	at hudson.model.User.get(User.java:441)
	at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.getAuthentication(CpsFlowExecution.java:614)
	at org.jenkinsci.plugins.workflow.cps.CpsVmThread.run(CpsVmThread.java:20)