Do you have a full stack trace for this? If you run composer with -v it should print it.

Should be fixed but I'm still interested to see a stack trace if you have one.

Well, now I can't reproduce it. I apologize, I might have been using a snapshot due to (composer/composer#10631), and this morning I updated composer to 2.3.2.

I see, no worries.

Isn't the real fix here to fix the caller that is making the invalid call. Not valid to call a function typed as string, with null?

Caller has been fixed in composer already, but IMO this is still good to do to mimick a type hint, which would type juggle null into string as well. I don't want to drop 5.3 support just yet in this lib to avoid having to maintain too many branches.

I am using version 2.2.6 with PHP8.1.13

Deprecation Notice: trim(): Passing null to parameter #1 ($string) of type string is deprecated in phar://C:/ProgramData/ComposerSetup/bin/composer.phar/vendor/composer/semver/src/VersionParser.php:105
Stack trace:
phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/Repository/PlatformRepository.php:671
phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/Repository/PlatformRepository.php:239
phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/Repository/ArrayRepository.php:311
phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/Installer.php:894
phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/Installer.php:428
phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/Installer.php:279
phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/Command/UpdateCommand.php:248
phar://C:/ProgramData/ComposerSetup/bin/composer.phar/vendor/symfony/console/Command/Command.php:245
phar://C:/ProgramData/ComposerSetup/bin/composer.phar/vendor/symfony/console/Application.php:835
phar://C:/ProgramData/ComposerSetup/bin/composer.phar/vendor/symfony/console/Application.php:185
phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/Console/Application.php:336
phar://C:/ProgramData/ComposerSetup/bin/composer.phar/vendor/symfony/console/Application.php:117
phar://C:/ProgramData/ComposerSetup/bin/composer.phar/src/Composer/Console/Application.php:131
phar://C:/ProgramData/ComposerSetup/bin/composer.phar/bin/composer:83
C:\ProgramData\ComposerSetup\bin\composer.phar:29

The latest 2.2.x release of Composer is 2.2.18, not 2.2.6. Please try to use the latest version.