\Drupal\Tests\system\Functional\Pager\PagerTest::testMultiplePagers() causes deprecations on PHP 8.1

Problem/Motivation

\Drupal\Tests\system\Functional\Pager\PagerTest::testMultiplePagers causes deprecations on PHP 8.1 because of query string used as NULL but later it used in string functions

See #3220021: [meta] Ensure compatibility of Drupal 9 with PHP 8.1 (as it evolves) and commit https://git.drupalcode.org/project/drupal/-/merge_requests/937/diffs?com... for credits

Steps to reproduce

Run core/modules/system/tests/src/Functional/Pager/PagerTest.php on PHP 8.1

  1x: str_replace(): Passing null to parameter #3 ($subject) of type array|string is deprecated
    1x in PagerTest::testMultiplePagers from Drupal\Tests\system\Functional\Pager

Proposed resolution

Fix the test data

Remaining tasks

review/commit

User interface changes

no

API changes

no

Data model changes

no

Release notes snippet

no