Polish merge script, use old title if input is null
Polish merge script, use old title if input is null

DR-YangLong/RocketMQ,penghuazhou/incubator-rocketmq,vsair/incubator-rocketmq,vsair/incubator-rocketmq,vsair/incubator-rocketmq,shroman/incubator-rocketmq,vesense/incubator-rocketmq,lindzh/incubator-rocketmq,vesense/incubator-rocketmq,lindzh/incubator-rocketmq,shroman/incubator-rocketmq,penghuazhou/incubator-rocketmq,lindzh/incubator-rocketmq,shroman/incubator-rocketmq,Vansee/RocketMQ,vesense/incubator-rocketmq,DR-YangLong/RocketMQ,penghuazhou/incubator-rocketmq