我们使用apacheflume将数据索引到elasticsearch中。
最近我们面临着这个例外。

org.elasticsearch.common.jackson.core.JsonGenerationException: No current event to copy
        at org.elasticsearch.common.jackson.core.JsonGenerator._reportError(JsonGenerator.java:1487)
        at org.elasticsearch.common.jackson.core.JsonGenerator.copyCurrentStructure(JsonGenerator.java:1390)
        at org.elasticsearch.common.xcontent.json.JsonXContentGenerator.copyCurrentStructure(JsonXContentGenerator.java:332)
        at org.elasticsearch.common.xcontent.XContentBuilder.copyCurrentStructure(XContentBuilder.java:1105)
        at org.apache.flume.sink.elasticsearch.ContentBuilderUtil.addComplexField(ContentBuilderUtil.java:63)
        at org.apache.flume.sink.elasticsearch.ContentBuilderUtil.appendField(ContentBuilderUtil.java:47)
        at org.jai.flume.sinks.elasticsearch.serializer.ElasticSearchJsonBodyEventSerializer.appendHeaders(ElasticSearchJsonBodyEventSerializer.java:48)
        at org.jai.flume.sinks.elasticsearch.serializer.ElasticSearchJsonBodyEventSerializer.getContentBuilder(ElasticSearchJsonBodyEventSerializer.java:35)
        at org.apache.flume.sink.elasticsearch.client.ElasticSearchTransportClient.addEvent(ElasticSearchTransportClient.java:164)
        at org.css.cssElasticsearchSink.process(cssElasticsearchSink.java:121)
        at org.apache.flume.sink.DefaultSinkProcessor.process(DefaultSinkProcessor.java:68)
        at org.apache.flume.SinkRunner$PollingRunner.run(SinkRunner.java:147)
        at java.lang.Thread.run(Thread.java:745)
2015-10-15 12:32:36,402 ERROR org.apache.flume.SinkRunner: Unable to deliver event. Exception follows.
org.apache.flume.EventDeliveryException: Failed to commit transaction. Transaction rolled back.
        at org.css.cssElasticsearchSink.process(cssElasticsearchSink.java:166)
        at org.apache.flume.sink.DefaultSinkProcessor.process(DefaultSinkProcessor.java:68)
        at org.apache.flume.SinkRunner$PollingRunner.run(SinkRunner.java:147)
        at java.lang.Thread.run(Thread.java:745)
Caused by: org.elasticsearch.common.jackson.core.JsonGenerationException: No current event to copy
        at org.elasticsearch.common.jackson.core.JsonGenerator._reportError(JsonGenerator.java:1487)
        at org.elasticsearch.common.jackson.core.JsonGenerator.copyCurrentStructure(JsonGenerator.java:1390)
        at org.elasticsearch.common.xcontent.json.JsonXContentGenerator.copyCurrentStructure(JsonXContentGenerator.java:332)
        at org.elasticsearch.common.xcontent.XContentBuilder.copyCurrentStructure(XContentBuilder.java:1105)
        at org.apache.flume.sink.elasticsearch.ContentBuilderUtil.addComplexField(ContentBuilderUtil.java:63)
        at org.apache.flume.sink.elasticsearch.ContentBuilderUtil.appendField(ContentBuilderUtil.java:47)
        at org.jai.flume.sinks.elasticsearch.serializer.ElasticSearchJsonBodyEventSerializer.appendHeaders(ElasticSearchJsonBodyEventSerializer.java:48)
        at org.jai.flume.sinks.elasticsearch.serializer.ElasticSearchJsonBodyEventSerializer.getContentBuilder(ElasticSearchJsonBodyEventSerializer.java:35)
        at org.apache.flume.sink.elasticsearch.client.ElasticSearchTransportClient.addEvent(ElasticSearchTransportClient.java:164)
        at org.css.cssElasticsearchSink.process(cssElasticsearchSink.java:121)

这个例外的原因是什么？它是一个格式错误的json对象吗？
Flume版本：1.5.0-cdh5.3.2
elasticsearch版本：“1.5.2”