I was attempting to trigger a build using the System Groovy Script with the following method call:

item.scheduleBuild2(0, new Cause.UpstreamCause(build), new ParametersAction(null))

The passing of null should cause an NPE, but because of this all jobs that were submitted from then on were stuck in our Build Queue. In order to fix it we had to bounce our Jenkins instance.

Initial Stack Trace:
SEVERE: Timer task hudson.model.LoadStatistics$LoadStatisticsUpdater@1b2ee745 failed
java.lang.NullPointerException
at hudson.model.ParametersAction.getAssignedLabel(ParametersAction.java:140)
at hudson.model.Queue$Item.getAssignedLabelFor(Queue.java:2079)
at hudson.model.Label$1.matches(Label.java:120)
at hudson.model.LoadStatistics.computeSnapshot(LoadStatistics.java:361)
at hudson.model.LoadStatistics$LoadStatisticsUpdater.doRun(LoadStatistics.java:395)
at hudson.triggers.SafeTimerTask.run(SafeTimerTask.java:50)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:304)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:178)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:724)

Stack Traces that occurred on all other jobs is attached.