The two abnormal situations of obtaining dynamic configuration that does not exist and exceptions should better be distinguished.

[tunefun]

What would you like to be added?

Currently: the obtained dynamic configuration does not exist or an exception returns null, which cannot be distinguished. com.huaweicloud.sermant.core.service.dynamicconfig.api.KeyService#getConfig
Required: An exception is thrown when the dynamic configuration fails to be obtained.

Why is this needed?

The plugin needs to perform different operations when it is exceptional or when it is null.