registry.conf中配置中心使用nacos时，namespace不能使用自定义的，只能设置为""，否则就会报错the {store.db.driverClassName} can't be empty

在nacos的public命名空间和自定义命名空间中，创建两个完全一样的seataServer.properties配置文件，在registry.conf中使用nacos作为配置中心时，配置namespace为自定义的命名空间ID，就会报错the {store.db.driverClassName} can't be empty，修改成""之后又可能正常启动

Start with the registry.conf Nacos configuration and reproduce the issue using identical seataServer.properties files in the public and custom namespaces. Trace how the configured namespace is used to load store.db.driverClassName, then verify that startup succeeds with the custom namespace and that the reported empty-value error no longer occurs.

Written by the indexing model from the issue text.