Issue #3427999 by andypost, Ayesh, bbrala: [PHP 8.4] Fix implicitly nullable type declarations

core/lib/Drupal/Core/Command/GenerateTheme.php

core/lib/Drupal/Core/Config/ConfigCollectionInfo.php

core/lib/Drupal/Core/Config/ConfigInstaller.php

core/lib/Drupal/Core/Config/ConfigInstallerInterface.php

core/lib/Drupal/Core/Config/ConfigManager.php

core/lib/Drupal/Core/Config/ConfigModuleOverridesEvent.php

core/lib/Drupal/Core/Config/Entity/ConfigEntityStorage.php

...rupal/Core/Config/Entity/ConfigEntityStorageInterface.php

core/lib/Drupal/Core/Config/Entity/ConfigEntityUpdater.php

core/lib/Drupal/Core/Config/Schema/Mapping.php

core/lib/Drupal/Core/Config/StorageComparer.php

core/lib/Drupal/Core/Config/TypedConfigManager.php

core/lib/Drupal/Core/Database/Query/Merge.php

core/lib/Drupal/Core/Database/Query/Select.php

core/lib/Drupal/Core/Database/Query/SelectExtender.php

core/lib/Drupal/Core/Database/Query/SelectInterface.php

core/lib/Drupal/Core/Database/Query/Update.php

core/lib/Drupal/Core/Database/RowCountException.php

core/lib/Drupal/Core/Database/StatementInterface.php

core/lib/Drupal/Core/Database/StatementPrefetchIterator.php