Second attempt at an NPE fix.
java.lang.NullPointerException
	at jenkins.slaves.iterators.api.NodeIterator$MetaNodeIterator.<init>(NodeIterator.java:185)
	at jenkins.slaves.iterators.api.NodeIterator.iterator(NodeIterator.java:76)
	at jenkins.slaves.iterators.api.NodeIterator$NodeIterable.iterator(NodeIterator.java:259)
	at …