Fix "Using null as an array offset is deprecated, use an empty string instead"

Author: thekid

ChangeLog.md

@@ -3,6 +3,9 @@ XP Compiler ChangeLog
 
 ## ?.?.? / ????-??-??
 
+* Fixed the warning *Using null as an array offset is deprecated, use an
+  empty string instead* in PHP 8.5+
+  (@thekid)
 * Fixed the error *Arrow functions on the right hand side of |> must be
   parenthesized* - see https://externals.io/message/128473#128554
   (@thekid)

src/main/php/lang/ast/emit/php/XpMeta.class.php

@@ -32,7 +32,7 @@ protected function annotations($result, $annotations, $resolve= null) {
       } else if (1 === sizeof($arguments) && isset($arguments[0])) {
         $this->emitOne($result, $arguments[0]);
         $result->out->write(',');
-        $lookup[$name][$resolve]= 1; // Resolve ambiguity
+        $lookup[$name][$resolve ?? '']= 1; // Resolve ambiguity
       } else {
         $result->out->write('[');
         foreach ($arguments as $name => $argument) {