Apache storm Apache storm final bolt不应该发出元组？

假设我们有以下拓扑

spout A -> bolt B -> bolt C -> bolt E

而螺栓E是最后一个，它将信息持久化到数据库中，因此不需要发出任何元组。如何实施这样的解决方案,

如果我定义了no输出\u字段，那么我会得到异常

Exception in thread "main" java.io.IOException: org.apache.storm.thrift.protocol.TProtocolException: Required field 'output_fields' is unset! Struct:StreamInfo(output_fields:null, direct:false)
        at storm.petrel.ThriftReader.read(ThriftReader.java:77)
        at storm.petrel.GenericTopology.readTopology(GenericTopology.java:36)
        at storm.petrel.GenericTopology.main(GenericTopology.java:53)
Caused by: org.apache.storm.thrift.protocol.TProtocolException: Required field 'output_fields' is unset! Struct:StreamInfo(output_fields:null, direct:false)
        at org.apache.storm.generated.StreamInfo.validate(StreamInfo.java:407)
        at org.apache.storm.generated.StreamInfo$StreamInfoStandardScheme.read(StreamInfo.java:485)
        at org.apache.storm.generated.StreamInfo$StreamInfoStandardScheme.read(StreamInfo.java:441)
        at org.apache.storm.generated.StreamInfo.read(StreamInfo.java:377)
        at org.apache.storm.generated.ComponentCommon$ComponentCommonStandardScheme.read(ComponentCommon.java:681)
        at org.apache.storm.generated.ComponentCommon$ComponentCommonStandardScheme.read(ComponentCommon.java:636)
        at org.apache.storm.generated.ComponentCommon.read(ComponentCommon.java:552)
        at org.apache.storm.generated.Bolt$BoltStandardScheme.read(Bolt.java:451)
        at org.apache.storm.generated.Bolt$BoltStandardScheme.read(Bolt.java:427)
        at org.apache.storm.generated.Bolt.read(Bolt.java:358)
        at org.apache.storm.generated.StormTopology$StormTopologyStandardScheme.read(StormTopology.java:727)
        at org.apache.storm.generated.StormTopology$StormTopologyStandardScheme.read(StormTopology.java:683)
        at org.apache.storm.generated.StormTopology.read(StormTopology.java:595)
        at storm.petrel.ThriftReader.read(ThriftReader.java:75)
        ... 2 more

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请重新检查螺栓E，确保其未被任何其他螺栓设置（这意味着螺栓E未被任何方法TopologyBuilder.setBolt使用，例如：TopologyBuilder.setBolt（“mybolt”，new mybolt（））。字段分组（“螺栓E”， 新字段（新字符串[]{“user_id”}）