Update all isset()? to ??

All the old isset($var) ? $var : <other> have been changed to $var ??
<other>

www/admin/phan_test.php

@@ -0,0 +1,9 @@
+<?php declare(strict_types=1);
+
+require 'config.php';
+require BASE.INCLUDES.'admin_header.php';
+
+// $DATA['foo'] = 'bar';
+// $messages['foo'] = 'bar';
+
+// __END__