PHP 8.5: Fix null array key creating a Nuance Source master
Summary: Setting null as an array key is deprecated since PHP 8.5 per https://www.php.net/releases/8.5/en.php: "Using null as an array offset or when calling array_key_exists() is now deprecated. Use an empty string instead." ``` ERROR 8192: Using null as an array offset is deprecated, use an empty string instead at [/var/www/html/phorge/phorge/src/applications/nuance/controller/NuanceSourceEditController.php:18] ``` Closes T16531 Test Plan: * PHP 8.5 * `./bin/config set phabricator.show-prototypes true` * Go to http://phorge.localhost/nuance/source/edit/form/default/ Reviewers: O1 Blessed Committers, valerio.bozzolan Reviewed By: O1 Blessed Committers, valerio.bozzolan Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno Maniphest Tasks: T16531 Differential Revision: https://we.phorge.it/D26806