refactor(json): use default config file if the user config is empty

[ghost]

there is technically nothing wrong with the users config file if its empty :)

[CarterLi]

I don't like the change. You read config files twice unnecessarily. Meanwhile, I don't like your habbit.

there is technically nothing wrong with the users config file if its empty

An empty string is not a valid JSON string, same as "" != NULL. Just remove the file.