NPE in ReplicationZKLockCleanerChore

While I am watching HMaster log, I found NullPointerException Logs.
This occurs every minute.

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2017-07-06 09:05:02,579 DEBUG [,1498445640728_ChoreService_1] cleaner.CleanerChore: Removing: hdfs://*** from archive
2017-07-06 09:05:02,585 ERROR [,1498445640728_ChoreService_2] hbase.ScheduledChore: Caught error
java.lang.NullPointerException
at org.apache.hadoop.hbase.master.cleaner.ReplicationZKLockCleanerChore.chore(ReplicationZKLockCleanerChore.java:80)
at org.apache.hadoop.hbase.ScheduledChore.run(ScheduledChore.java:185)
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 org.apache.hadoop.hbase.JitterScheduledThreadPoolExecutorImpl$JitteredRunnableScheduledFuture.run(JitterScheduledThreadPoolExecutorImpl.java:110)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
2017-07-06 09:05:02,585 DEBUG [,1498445640728_ChoreService_1] cleaner.CleanerChore: Removing: hdfs://*** from archive
2017-07-06 09:05:02,586 DEBUG [,1498445640728_ChoreService_1] cleaner.CleanerChore: Removing: hdfs://*** from archive

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Here is related code:
List<String> replicators = queues.getListOfReplicators();
for (String replicator: replicators) {