topology运行一段时间后报错，求探讨

[鱿鱼ing]

kafka的topic有3个分区，在topology里并行度也设置成3，运行一段时间后报了下面的错，这是为什么？

[ERROR 2016-09-15 19:13:46 c.a.j.t.e.s.SpoutExecutors:186 attachmentSpout:10-MultipleThreadSpoutExecutors] spout execute error 
java.lang.NullPointerException: null
	at java.util.TreeMap.fixAfterInsertion(TreeMap.java:2291) ~[na:1.8.0_20]
	at java.util.TreeMap.put(TreeMap.java:582) ~[na:1.8.0_20]
	at java.util.TreeSet.add(TreeSet.java:255) ~[na:1.8.0_20]
	at storm.kafka.PartitionManager.fill(PartitionManager.java:210) ~[storm-kafka-0.9.6.jar:0.9.6]
	at storm.kafka.PartitionManager.next(PartitionManager.java:124) ~[storm-kafka-0.9.6.jar:0.9.6]
	at storm.kafka.KafkaSpout.nextTuple(KafkaSpout.java:141) ~[storm-kafka-0.9.6.jar:0.9.6]
	at com.alibaba.jstorm.task.execute.spout.SpoutExecutors.nextTuple(SpoutExecutors.java:183) ~[jstorm-core-2.1.0.jar:na]
	at com.alibaba.jstorm.task.execute.spout.MultipleThreadSpoutExecutors.run(MultipleThreadSpoutExecutors.java:79) [jstorm-core-2.1.0.jar:na]
	at com.alibaba.jstorm.callback.AsyncLoopRunnable.run(AsyncLoopRunnable.java:95) [jstorm-core-2.1.0.jar:na]
	at java.lang.Thread.run(Thread.java:745) [na:1.8.0_20]
[ERROR 2016-09-15 19:13:46 c.a.j.t.e.TaskReportError:46 attachmentSpout:10-MultipleThreadSpoutExecutors] Report error to /ZK/taskerrors/test913-70-1473755909/10

java.lang.NullPointerException: null
	at java.util.TreeMap.fixAfterInsertion(TreeMap.java:2291) ~[na:1.8.0_20]
	at java.util.TreeMap.put(TreeMap.java:582) ~[na:1.8.0_20]
	at java.util.TreeSet.add(TreeSet.java:255) ~[na:1.8.0_20]
	at storm.kafka.PartitionManager.fill(PartitionManager.java:210) ~[storm-kafka-0.9.6.jar:0.9.6]
	at storm.kafka.PartitionManager.next(PartitionManager.java:124) ~[storm-kafka-0.9.6.jar:0.9.6]
	at storm.kafka.KafkaSpout.nextTuple(KafkaSpout.java:141) ~[storm-kafka-0.9.6.jar:0.9.6]
	at com.alibaba.jstorm.task.execute.spout.SpoutExecutors.nextTuple(SpoutExecutors.java:183) ~[jstorm-core-2.1.0.jar:na]
	at com.alibaba.jstorm.task.execute.spout.MultipleThreadSpoutExecutors.run(MultipleThreadSpoutExecutors.java:79) [jstorm-core-2.1.0.jar:na]
	at com.alibaba.jstorm.callback.AsyncLoopRunnable.run(AsyncLoopRunnable.java:95) [jstorm-core-2.1.0.jar:na]
	at java.lang.Thread.run(Thread.java:745) [na:1.8.0_20]