'Type mismatch' error after update to 4.1.*

[AlinaSob]

API Platform version(s) affected: 4.1.* (although I do not know why it hadn't appeared earlier)

Description
After upgrading my in-developent app from api-platform 3.4 to 4.1 I've got plenty of similar errors:

TypeError: ApiPlatform\OpenApi\Model\Tag::getExternalDocs(): Return value must be of type string, null returned in /path_to_app/vendor/api-platform/openapi/Model/Tag.php on line 52

How to reproduce
In my case - just upgrade and open your_domain/api

Possible Solution
The return type should clearly be ?string in api-platform/openapi/Model/Tag.php on line 52 as the property is null by default

[soyuka]

thanks!