[Validator] try to call __get method if property is uninitialized

src/Symfony/Component/Validator/Mapping/PropertyMetadata.php

@@ -50,8 +50,21 @@ class PropertyMetadata extends MemberMetadata
     {
         $reflProperty = $this->getReflectionMember($object);
 
-        if (\PHP_VERSION_ID >= 70400 && !$reflProperty->isInitialized($object)) {
-            return null;
+        if (\PHP_VERSION_ID >= 70400 && $reflProperty->hasType() && !$reflProperty->isInitialized($object)) {
+            // There is no way to check if a property has been unset or if it is uninitialized.
+            // When trying to access an uninitialized property, __get method is triggered.
+
+            // If __get method is not present, no fallback is possible
+            // Otherwise we need to catch an Error in case we are trying to access an uninitialized but set property.
+            if (!method_exists($object, '__get')) {
+                return null;
+            }
+
+            try {
+                return $reflProperty->getValue($object);
+            } catch (\Error $e) {
+                return null;
+            }
         }
 
         return $reflProperty->getValue($object);

src/Symfony/Component/Validator/Tests/Fixtures/Entity_74_Proxy.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace Symfony\Component\Validator\Tests\Fixtures;
+
+class Entity_74_Proxy extends Entity_74
+{
+    public string $notUnset;
+
+    public function __construct()
+    {
+        unset($this->uninitialized);
+    }
+
+    public function __get($name)
+    {
+        return 42;
+    }
+}

src/Symfony/Component/Validator/Tests/Mapping/PropertyMetadataTest.php

@@ -15,11 +15,13 @@ use PHPUnit\Framework\TestCase;
 use Symfony\Component\Validator\Mapping\PropertyMetadata;
 use Symfony\Component\Validator\Tests\Fixtures\Entity;
 use Symfony\Component\Validator\Tests\Fixtures\Entity_74;
+use Symfony\Component\Validator\Tests\Fixtures\Entity_74_Proxy;
 
 class PropertyMetadataTest extends TestCase
 {
     const CLASSNAME = 'Symfony\Component\Validator\Tests\Fixtures\Entity';
     const CLASSNAME_74 = 'Symfony\Component\Validator\Tests\Fixtures\Entity_74';
+    const CLASSNAME_74_PROXY = 'Symfony\Component\Validator\Tests\Fixtures\Entity_74_Proxy';
     const PARENTCLASS = 'Symfony\Component\Validator\Tests\Fixtures\EntityParent';
 
     public function testInvalidPropertyName()
@@ -66,4 +68,17 @@ class PropertyMetadataTest extends TestCase
 
         $this->assertNull($metadata->getPropertyValue($entity));
     }
+
+    /**
+     * @requires PHP 7.4
+     */
+    public function testGetPropertyValueFromUninitializedPropertyShouldNotReturnNullIfMagicGetIsPresent()
+    {
+        $entity = new Entity_74_Proxy();
+        $metadata = new PropertyMetadata(self::CLASSNAME_74_PROXY, 'uninitialized');
+        $notUnsetMetadata = new PropertyMetadata(self::CLASSNAME_74_PROXY, 'notUnset');
+
+        $this->assertNull($notUnsetMetadata->getPropertyValue($entity));
+        $this->assertEquals(42, $metadata->getPropertyValue($entity));
+    }
 }