[JENKINS-20769] Trying to fix/suppress some related observed or actual NPEs.
java.lang.NullPointerException
	at hudson.remoting.ProxyOutputStream$Flush$1.run(ProxyOutputStream.java:305)
	at hudson.remoting.PipeWriter$1.run(PipeWriter.java:158)
	at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
	at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
	at java.util.concurrent.FutureTask.run(Unknown Source)
	at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:111)