Updated to a more current LTS parent.
Defense against an observed NPE during startup.
java.lang.NullPointerException
	at jenkins.slaves.iterators.api.NodeIterator$MetaNodeIterator.<init>(NodeIterator.java:182)
	at jenkins.slaves.iterators.api.NodeIterator.iterator(NodeIterator.java:75)
	at jenkins.slaves.iterators.api.NodeIterator$NodeIterable.iterator(NodeIterator.java:256)
	at …
Fixed some stylistic warnings.