NullPointerException at Maps.doDifference at DOMRpcRouter during SingleFeatureTest

https://git.opendaylight.org/gerrit/#/c/50638/ build, a totally unrelated minor change, failed with this, which I'm 99% sure is unrelated to the simple cosmetic Checkstyle compliance related changes made in that Gerrit, so I suspect that this could be some sort of hard to reproduce Heisenbug, but let me still record it here before just doing a "recheck", in case others see this more often in the future:

18:20:03 Running org.opendaylight.odlparent.featuretest.SingleFeatureTest
18:24:05 Tests run: 6, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 240.727 sec <<< FAILURE! - in org.opendaylight.odlparent.featuretest.SingleFeatureTest
18:24:05 installFeature(org.opendaylight.odlparent.featuretest.SingleFeatureTest)[repoUrl: file:/w/workspace/genius-verify-carbon-mvn33-openjdk8/features/target/classes/features.xml, Feature: odl-genius-fcaps-application 0.2.0-SNAPSHOT] Time elapsed: 28.484 sec <<< ERROR!
18:24:05 java.lang.NullPointerException
18:24:05 at com.google.common.collect.Maps.doDifference(Maps.java:428)
18:24:05 at com.google.common.collect.Maps.difference(Maps.java:419)
18:24:05 at com.google.common.collect.Maps.difference(Maps.java:387)
18:24:05 at org.opendaylight.controller.md.sal.dom.broker.impl.DOMRpcRouter$Registration.addRpc(DOMRpcRouter.java:185)
18:24:05 at org.opendaylight.controller.md.sal.dom.broker.impl.DOMRpcRouter.notifyAdded(DOMRpcRouter.java:109)
18:24:05 at org.opendaylight.controller.md.sal.dom.broker.impl.DOMRpcRouter.lambda$registerRpcImplementation$1(DOMRpcRouter.java:87)
18:24:05 at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
18:24:05 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
18:24:05 at java.lang.Thread.run(Thread.java:745)
18:24:05
18:24:05
18:24:05 Results :
18:24:05
18:24:05 Tests in error:
18:24:05 null