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.

ERROR 8192: strlen(): Passing null to parameter #1 ($string) of type string is deprecated at [/var/www/html/phorge/phorge/src/applications/files/management/PhabricatorFilesManagementMigrateWorkflow.php:65]

Run ../phorge/bin/files migrate: Get no strlen() error anymore but only expected output Usage Exception: Specify an engine to migrate to with --engine`. Use files engines to get a list of engines.`