private void chkAndRmvBlankParentNode(String parentNode) {
        List<String> nodeSet = ZKUtil.getChildren(zkw, parentNode);
        if (nodeSet != null && nodeSet.isEmpty()) {
            ZKUtil.delZNode(this.zkw, parentNode);
        }
    }
Get offset stored in zookeeper, if not found or error, set null

@param groupTopicPartMap   the group topic-partition map
inlong-tubemq/tubemq-server/src/main/java/org/apache/inlong/tubemq/server/broker/offset/offsetstorage/ZkOffsetStorage.java