Add more nullsafe operators

Author: nicolas-grekas

Caster/Caster.php

@@ -61,7 +61,7 @@ public static function castObject(object $obj, string $class, bool $hasDebugInfo
 
         if ($a) {
             static $publicProperties = [];
-            $debugClass = $debugClass ?? get_debug_type($obj);
+            $debugClass ??= get_debug_type($obj);
 
             $i = 0;
             $prefixedKeys = [];