Error when adding flag mapping for country

Problem/Motivation

Unexpected error when mapping country to a flag

Attached the sequence of screenshots and error log.

Steps to reproduce

-Fresh install of Drupal 11.3.6
-Add the Country module and enable it
-Add the Flags module and enable it
-Create a custom content type with the Country field
-Create a new content, select a country from the list, save the content
-Configure a flag mapping, click 'Create Mapping', error will occur

Proposed resolution

Remaining tasks

User interface changes

No User

API changes

No API change.

Data model changes

No data model changes. Using the Flags and Country modules as is.