mongodbReader读取报错列数不匹配

```
经DataX智能分析,该任务最可能的错误原因是:
com.alibaba.datax.common.exception.DataXException: Code:[DBUtilErrorCode-00], Description:[您的配置错误.]. - 列配置信息有错误. 因为您配置的 任务中，源头读取字段数:0 与 目的表要写入的字段数:1 不相等. 请检查您的配置并作出修改.
at com.alibaba.datax.common.exception.DataXException.asDataXException(DataXException.java:26)
at com.alibaba.datax.plugin.rdbms.writer.CommonRdbmsWriter$Task.startWriteWithConnection(CommonRdbmsWriter.java:278)
at com.alibaba.datax.plugin.rdbms.writer.CommonRdbmsWriter$Task.startWrite(CommonRdbmsWriter.java:319)
at com.alibaba.datax.plugin.writer.mysqlwriter.MysqlWriter$Task.startWrite(MysqlWriter.java:78)
at com.alibaba.datax.core.taskgroup.runner.WriterRunner.run(WriterRunner.java:56)
at java.lang.Thread.run(Unknown Source)
```
是否是因为mongo内该字段不存在或者为null？但是我已经在query加了条件限制字段非null且存在，求大佬指导一下

Start with the reported stack trace in DataXException.java, CommonRdbmsWriter.java, MysqlWriter.java, and WriterRunner.java, then inspect the MongoDB reader and the task configuration mentioned in the issue. Reproduce the task with the non-null and exists query conditions, compare the source and destination field counts, and document the confirmed cause and configuration or code change needed.

Written by the indexing model from the issue text.