请问adapter rocketmq客户端连接报错的原因是什么

报错信息:

2018-11-27 15:55:50.992 INFO 3461 --- [ Thread-4] c.a.o.c.a.l.l.CanalAdapterRocketMQWorker : =============> Start to connect topic: example <============= 2018-11-27 15:55:50.993 INFO 3461 --- [ Thread-4] c.a.o.c.a.l.l.CanalAdapterRocketMQWorker : =============> Start to subscribe topic: example<============= 2018-11-27 15:55:50.993 INFO 3461 --- [ Thread-4] c.a.o.c.a.l.l.CanalAdapterRocketMQWorker : =============> Subscribe topic: example succeed<============= 2018-11-27 15:55:51.094 ERROR 3461 --- [ Thread-4] c.a.o.c.a.l.l.CanalAdapterRocketMQWorker : null java.lang.NullPointerException: null at com.alibaba.otter.canal.client.rocketmq.RocketMQCanalConnector.ack(RocketMQCanalConnector.java:219) ~[canal.client-1.1.2-SNAPSHOT.jar:na] at com.alibaba.otter.canal.adapter.launcher.loader.AbstractCanalAdapterWorker.mqWriteOutData(AbstractCanalAdapterWorker.java:152) ~[client-adapter.launcher-1.1.2-SNAPSHOT.jar:na] at com.alibaba.otter.canal.adapter.launcher.loader.CanalAdapterRocketMQWorker.process(CanalAdapterRocketMQWorker.java:64) ~[client-adapter.launcher-1.1.2-SNAPSHOT.jar:na] at java.lang.Thread.run(Thread.java:748) ~[na:1.8.0_191]

配置文件application.yml:

server: port: 8081 logging: level: org.springframework: WARN com.alibaba.otter.canal.client.adapter.rdb: DEBUG spring: jackson: date-format: yyyy-MM-dd HH:mm:ss time-zone: GMT+8 default-property-inclusion: non_null canal.conf: zookeeperHosts: 127.0.0.1:2181 mqServers: 127.0.0.1:9876 flatMessage: true retries: 0 timeout: mqTopics: - mqMode: rocketmq topic: example groups: - groupId: g2 outAdapters: - name: rdb key: mysql properties: jdbc.driverClassName: com.mysql.jdbc.Driver jdbc.url: jdbc:mysql://127.0.0.1:3306 jdbc.username: root jdbc.password:************ threads: 5 commitSize: 5000

原提问者GitHub用户Near-Zhang