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.

strlen(): Passing null to parameter #1 ($string) of type string is deprecated
#0 PhabricatorOAuthServerTokenController::handleRequest(AphrontRequest) called at [<phorge>/src/aphront/configuration/AphrontApplicationConfiguration.php:284]

See Q182

Read the code. strlen is used to get the length of an existing string and not to check for emptiness of a string. There is no string length comparison in the existing code.