NullPointerException in ParserUtils.parseConfig if config is missing <final> element

[erwa]

Currently, ParserUtils assumes that each <property> in the job config has the following 4 subelements:

• <name>
• <value>
• <final>
• <source>

<final> may not always be present, causing a NPE:

2019-06-06 00:13:10,516 [ERROR] from history.HistoryFileMover in pool-4-thread-1 - Encountered exception while moving history directories
java.lang.NullPointerException: null
        at com.linkedin.tony.util.ParserUtils.parseConfig(ParserUtils.java:214)
        at cache.CacheWrapper.updateCaches(CacheWrapper.java:90)
        at history.HistoryFileMover.moveIntermediateToFinished(HistoryFileMover.java:72)
        at history.HistoryFileMover.lambda$new$0(HistoryFileMover.java:62)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

To be more robust, we should add null checks.