Drupal\search\SearchPageRepository->getDefaultSearchPage()() (Line: 80) triggers deprecations in PHP 8.5

Problem/Motivation

Drupal\search\SearchPageRepository->getDefaultSearchPage()() (Line: 80) triggers deprecations because it uses NULL as an array key.

Steps to reproduce

Run \Drupal\Tests\search\Functional\SearchConfigSettingsFormTest::testMultipleSearchPages

Proposed resolution

Don't

Remaining tasks

User interface changes

None

Introduced terminology

N/a

API changes

None

Data model changes

None

Release notes snippet

N/a