DataWorks mysql到es同步时，会报这个错误，这是什么原因呢？

DataWorks mysql到es同步时，会报这个错误，这是什么原因呢？ java.io.IOException: Request POST ....../_bulk HTTP/1.1 yielded text/html, should be json: HTTP/1.1 502 Bad Gateway at io.searchbox.client.http.JestHttpClient.deserializeResponse(JestHttpClient.java:210) ~[jest-6.3.1.jar:na] at io.searchbox.client.http.JestHttpClient.execute(JestHttpClient.java:71) ~[jest-6.3.1.jar:na] at io.searchbox.client.http.JestHttpClient.execute(JestHttpClient.java:63) ~[jest-6.3.1.jar:na] at com.alibaba.datax.plugin.writer.elasticsearchwriter.ElasticSearchClient.execute(ElasticSearchClient.java:201) ~[elasticsearchwriter-0.0.1-SNAPSHOT.jar:na] at com.alibaba.datax.plugin.writer.elasticsearchwriter.ElasticSearchClient.bulkInsert(ElasticSearchClient.java:290) ~[elasticsearchwriter-0.0.1-SNAPSHOT.jar:na] at com.alibaba.datax.plugin.writer.elasticsearchwriter.ElasticSearchWriter$Task$2.call(ElasticSearchWriter.java:1002) ~[elasticsearchwriter-0.0.1-SNAPSHOT.jar:na] at com.alibaba.datax.plugin.writer.elasticsearchwriter.ElasticSearchWriter$Task$2.call(ElasticSearchWriter.java:999) ~[elasticsearchwriter-0.0.1-SNAPSHOT.jar:na] at com.alibaba.datax.common.util.RetryUtil$Retry.call(RetryUtil.java:163) ~[datax-common-0.0.1-SNAPSHOT.jar:na] at com.alibaba.datax.common.util.RetryUtil$Retry.doRetry(RetryUtil.java:111) ~[datax-common-0.0.1-SNAPSHOT.jar:na] at com.alibaba.datax.common.util.RetryUtil.executeWithRetry(RetryUtil.java:51) [datax-common-0.0.1-SNAPSHOT.jar:na] at com.alibaba.datax.plugin.writer.elasticsearchwriter.ElasticSearchWriter$Task.doBatchInsert(ElasticSearchWriter.java:999) [elasticsearchwriter-0.0.1-SNAPSHOT.jar:na] at com.alibaba.datax.plugin.writer.elasticsearchwriter.ElasticSearchWriter$Task.startWrite(ElasticSearchWriter.java:633) [elasticsearchwriter-0.0.1-SNAPSHOT.jar:na] at com.alibaba.datax.core.taskgroup.runner.WriterRunner.run(WriterRunner.java:114) [datax-core-0.0.1-SNAPSHOT.jar:na] at java.lang.Thread.run(Thread.java:834) [na:1.8.0_112] Caused by: com.google.gson.JsonSyntaxException: com.google.gson.stream.MalformedJsonException: Use JsonReader.setLenient(true) to accept malformed JSON at line 2 column 2 path $ at com.google.gson.JsonParser.parse(JsonParser.java:65) ~[gson-2.8.0.jar:na] at com.google.gson.JsonParser.parse(JsonParser.java:45) ~[gson-2.8.0.jar:na] at io.searchbox.action.AbstractAction.parseResponseBody(AbstractAction.java:103) ~[jest-common-6.3.1.jar:na] at io.searchbox.core.Bulk.createNewElasticSearchResult(Bulk.java:128) ~[jest-common-6.3.1.jar:na] at io.searchbox.core.Bulk.createNewElasticSearchResult(Bulk.java:123) ~[jest-common-6.3.1.jar:na] at io.searchbox.core.Bulk.createNewElasticSearchResult(Bulk.java:30) ~[jest-common-6.3.1.jar:na] at io.searchbox.client.http.JestHttpClient.deserializeResponse(JestHttpClient.java:197) ~[jest-6.3.1.jar:na] ... 13 common frames omitted Caused by: com.google.gson.stream.MalformedJsonException: Use JsonReader.setLenient(true) to accept malformed JSON at line 2 column 2 path $ at com.google.gson.stream.JsonReader.syntaxError(JsonReader.java:1559) ~[gson-2.8.0.jar:na] at com.google.gson.stream.JsonReader.checkLenient(JsonReader.java:1401) ~[gson-2.8.0.jar:na] at com.google.gson.stream.JsonReader.doPeek(JsonReader.java:542) ~[gson-2.8.0.jar:na] at com.google.gson.stream.JsonReader.peek(JsonReader.java:425) ~[gson-2.8.0.jar:na] at com.google.gson.JsonParser.parse(JsonParser.java:60) ~[gson-2.8.0.jar:na] ... 19 common frames omitted