strlen() was used in Phabricator to check if a generic value is a non-empty string.
This behavior is deprecated since PHP 8.1. Phorge adopts phutil_nonempty_string() as a replacement.

Note: this may highlight other absurd input values that might be worth correcting
instead of just ignoring. If phutil_nonempty_string() throws an exception in your
instance, report it to Phorge to evaluate and fix that specific corner case.

EXCEPTION: (RuntimeException) strlen(): Passing null to parameter #1 ($string) of type string is deprecated at [<arcanist>/src/error/PhutilErrorHandler.php:261]
arcanist(), ava(), phorge(), wmf-ext-misc()
  #0 <#2> PhutilErrorHandler::handleError(integer, string, string, integer) called at [<phorge>/applications/auth/provider/PhabricatorOAuth1AuthProvider.php:70]

EXCEPTION: (RuntimeException) strlen(): Passing null to parameter #1 ($string) of type string is deprecated at [<arcanist>/src/error/PhutilErrorHandler.php:261]
arcanist(), ava(), phorge(), wmf-ext-misc()
  #0 <#2> PhutilErrorHandler::handleError(integer, string, string, integer) called at [<phorge>/applications/auth/view/PhabricatorAuthAccountView.php:32]

Closes T15590

• As an admin, set up custom "MediaWiki" OAuth provider from from https://gitlab.wikimedia.org/-/ide/project/repos/phabricator/extensions/edit/wmf/stable/-/src/oauth/
• As an admin, apply D25373
• As a user, go to /auth/login/mediawiki:whatever/
• Select login button
• Allow authentication on third-party site
• Get redirected to Phorge instance

Phorge user account registration page "Create a New Account" at /auth/register/abcdefghijklmnopqrstuvwxyz0123456/ now renders as expected, instead of displaying errors only.