[VarExporter] fix proxy helper when a method returns null

Author: nikophil

ProxyHelper.php

@@ -311,7 +311,7 @@ public static function exportType(\ReflectionFunctionAbstract|\ReflectionPropert
             return '';
         }
         if (null === $glue) {
-            return (!$noBuiltin && $type->allowsNull() && 'mixed' !== $name ? '?' : '').$types[0];
+            return (!$noBuiltin && $type->allowsNull() && !\in_array($name, ['mixed', 'null'], true) ? '?' : '').$types[0];
         }
         sort($types);
 

Tests/Fixtures/LazyProxy/Php82NullStandaloneReturnType.php

@@ -0,0 +1,20 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\VarExporter\Tests\Fixtures\LazyProxy;
+
+class Php82NullStandaloneReturnType
+{
+    public function foo(): null
+    {
+        return null;
+    }
+}

Tests/ProxyHelperTest.php

@@ -14,6 +14,7 @@
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\VarExporter\Exception\LogicException;
 use Symfony\Component\VarExporter\ProxyHelper;
+use Symfony\Component\VarExporter\Tests\Fixtures\LazyProxy\Php82NullStandaloneReturnType;
 use Symfony\Component\VarExporter\Tests\Fixtures\LazyProxy\StringMagicGetClass;
 
 class ProxyHelperTest extends TestCase
@@ -188,6 +189,17 @@ public function testCannotGenerateGhostForStringMagicGet()
         $this->expectException(LogicException::class);
         ProxyHelper::generateLazyGhost(new \ReflectionClass(StringMagicGetClass::class));
     }
+
+    /**
+     * @requires PHP 8.2
+     */
+    public function testNullStandaloneReturnType()
+    {
+        self::assertStringContainsString(
+            'public function foo(): null',
+            ProxyHelper::generateLazyProxy(new \ReflectionClass(Php82NullStandaloneReturnType::class))
+        );
+    }
 }
 
 abstract class TestForProxyHelper