NPE in ListenSyslog processor when datagram size is zero

I have a 6 node cluster with an F5 load balancer in front to distribute UDP syslog load. It splits an incoming syslog stream and sends separate lines to each node in the cluster (I am checking if zero length datagrams are being sent from the F5 LB). However, from Bryan Bende from user mailing lists

>>>

Line 431 of ListenSyslog has the following code:

if (!valid || !event.isValid())

So to get an NPE there means event must be null, and event comes from this code:

boolean valid = true;
try {
event = parser.parseEvent(rawSyslogEvent.getData(), sender);
} catch (final ProcessException pe) {
getLogger().warn("Failed to parse Syslog event; routing to invalid");
valid = false;
}

The parser returns null if the bytes sent in are null or length 0.

We should be checking if (!valid || event == null || !event.isValid())
to avoid this case, and I think a similar situation exists in the
ParseSyslog processor. It appears this would only happen if parsing
messages is enabled in ListenSyslog.

<<<<

and log file snippet is

2017-04-25 17:43:07,549 ERROR [Timer-Driven Process Thread-2] o.a.n.processors.standard.ListenSyslog ListenSyslog[id=0a932c37-0158-1000-0000-0000656754bf] ListenSyslog[id=0a932c37-0158-1000-0000-0000656754bf] failed to process session due to java.lang.NullPointerException: java.lang.NullPointerException
2017-04-25 17:43:07,550 ERROR [Timer-Driven Process Thread-2] o.a.n.processors.standard.ListenSyslog
java.lang.NullPointerException: null
at org.apache.nifi.processors.standard.ListenSyslog.onTrigger(ListenSyslog.java:431) ~[na:na]
at org.apache.nifi.processor.AbstractProcessor.onTrigger(AbstractProcessor.java:27) ~[nifi-api-1.1.2.jar:1.1.2]
at org.apache.nifi.controller.StandardProcessorNode.onTrigger(StandardProcessorNode.java:1099) ~[nifi-framework-core-1.1.2.jar:1.1.2]
at org.apache.nifi.controller.tasks.ContinuallyRunProcessorTask.call(ContinuallyRunProcessorTask.java:136) [nifi-framework-core-1.1.2.jar:1.1.2]
at org.apache.nifi.controller.tasks.ContinuallyRunProcessorTask.call(ContinuallyRunProcessorTask.java:47) [nifi-framework-core-1.1.2.jar:1.1.2]
at org.apache.nifi.controller.scheduling.TimerDrivenSchedulingAgent$1.run(TimerDrivenSchedulingAgent.java:132) [nifi-framework-core-1.1.2.jar:1.1.2]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_51]
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) [na:1.8.0_51]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_51]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294) [na:1.8.0_51]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_51]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_51]
at java.lang.Thread.run(Thread.java:745) [na:1.8.0_51]
2017-04-25 17:43:07,550 WARN [Timer-Driven Process Thread-2] o.a.n.processors.standard.ListenSyslog ListenSyslog[id=0a932c37-0158-1000-0000-0000656754bf] Processor Administratively Yielded for 1 sec due to processing failure
2017-04-25 17:43:07,550 WARN [Timer-Driven Process Thread-2] o.a.n.c.t.ContinuallyRunProcessorTask Administratively Yielding ListenSyslog[id=0a932c37-0158-1000-0000-0000656754bf] due to uncaught Exception: java.lang.NullPointerException
2017-04-25 17:43:07,551 WARN [Timer-Driven Process Thread-2] o.a.n.c.t.ContinuallyRunProcessorTask
java.lang.NullPointerException: null
at org.apache.nifi.processors.standard.ListenSyslog.onTrigger(ListenSyslog.java:431) ~[na:na]
at org.apache.nifi.processor.AbstractProcessor.onTrigger(AbstractProcessor.java:27) ~[nifi-api-1.1.2.jar:1.1.2]
at org.apache.nifi.controller.StandardProcessorNode.onTrigger(StandardProcessorNode.java:1099) ~[nifi-framework-core-1.1.2.jar:1.1.2]
at org.apache.nifi.controller.tasks.ContinuallyRunProcessorTask.call(ContinuallyRunProcessorTask.java:136) [nifi-framework-core-1.1.2.jar:1.1.2]
at org.apache.nifi.controller.tasks.ContinuallyRunProcessorTask.call(ContinuallyRunProcessorTask.java:47) [nifi-framework-core-1.1.2.jar:1.1.2]
at org.apache.nifi.controller.scheduling.TimerDrivenSchedulingAgent$1.run(TimerDrivenSchedulingAgent.java:132) [nifi-framework-core-1.1.2.jar:1.1.2]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_51]
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308) [na:1.8.0_51]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_51]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294) [na:1.8.0_51]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_51]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_51]
at java.lang.Thread.run(Thread.java:745) [na:1.8.0_51]