[4.x]: Allow addresses to not have a default country code

[ryssbowh]

What happened?

Description

I've got a user facing form for saving addresses where they have to select their country, the client wants to force the users to choose one but start with an empty value.

When sending the form without country for validation I'm not getting an error on the country because it takes "US" by default, even though the user has not chosen one. Sending an empty string as countryCode does not replace the country in the address before it's validated.

I also tried to set an empty string to the config defaultCountryCode but I then get a 500 :

"name":"Exception"
"message":"Missing required property country_code."
"code":0
"error":"Missing required property country_code."
"exception":"InvalidArgumentException"
"file":"/var/www/html/vendor/commerceguys/addressing/src/AddressFormat/AddressFormat.php"
"line":120

Does this sound like a possible change ?

Steps to reproduce

1. set the config defaultCountryCode to an empty string
2. Save an address without country

Expected behavior

I'm getting a validation error "The country field is required"

Craft CMS version

4.12.1

PHP version

8.2

Operating system and version

No response

Database type and version

No response

Image driver and version

No response

Installed plugins and versions

[ryssbowh]

I'll also add another issue which I think is related: during the craft 4 migration of this site it happened that some addresses ended up without country, which made other services fail. The client and I could not figure out what was the problem because "US" was always chosen in the CP when in fact no country was chosen, it was just the default, which on a UX point of view is misleading

[brandonkelly]

I also tried to set an empty string to the config defaultCountryCode but I then get a 500 :

Craft 4.12.6 and 5.4.7 are out with a “fix” for that: now an InvalidConfigException will be thrown instead, which should make it more clear what the problem was. (#15812)