if `API_BASE_URL_KEY ` is set and assigned to `api_base_url`, but `use_default_value` is set to true, the `DEFAULT_API_BASE_URL ` won't be used because of the `||=`. Is that what you'd expect to happen?

As long as `= get_config(API_BASE_URL_KEY)` is returning any value other than nil `DEFAULT_API_BASE_URL ` will never be used.