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) Undefined index: above at [<arcanist>/src/error/PhutilErrorHandler.php:251]
 arcanist(), phorge()
   #0 <#2> PhutilErrorHandler::handleError(integer, string, string, integer, array) called at [<phorge>/src/applications/macro/engine/PhabricatorMemeEngine.php:276]

Closes T15637

Carefully read the code, keeping in mind that strlen does not accept passing null in PHP 8, and looking at what we did in rPb4cfe56f03b44615ac9251aed8d74bf13b085051.