bug symfony#54081 [DoctrineBridge] Safeguard dynamic access to Doctrine metadata properties (derrabus)

This PR was merged into the 5.4 branch.

Discussion
----------

[DoctrineBridge] Safeguard dynamic access to Doctrine metadata properties

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        | Fix symfony#54077
| License       | MIT

Commits
-------

9eadc22 Safeguard dynamic access to Doctrine metadata properties

Author: derrabus

src/Symfony/Bridge/Doctrine/Form/DoctrineOrmTypeGuesser.php

@@ -208,7 +208,7 @@ private static function getRealClass(string $class): string
     private static function getMappingValue($mapping, string $key)
     {
         if ($mapping instanceof JoinColumnMapping) {
-            return $mapping->$key;
+            return $mapping->$key ?? null;
         }
 
         return $mapping[$key] ?? null;

src/Symfony/Bridge/Doctrine/PropertyInfo/DoctrineExtractor.php

@@ -314,7 +314,7 @@ private function getPhpType(string $doctrineType): ?string
     private static function getMappingValue($mapping, string $key)
     {
         if ($mapping instanceof AssociationMapping || $mapping instanceof EmbeddedClassMapping || $mapping instanceof FieldMapping || $mapping instanceof JoinColumnMapping) {
-            return $mapping->$key;
+            return $mapping->$key ?? null;
         }
 
         return $mapping[$key] ?? null;

src/Symfony/Bridge/Doctrine/Validator/DoctrineLoader.php

@@ -148,7 +148,7 @@ private function getExistingUniqueFields(ClassMetadata $metadata): array
     private static function getFieldMappingValue($mapping, string $key)
     {
         if ($mapping instanceof FieldMapping) {
-            return $mapping->$key;
+            return $mapping->$key ?? null;
         }
 
         return $mapping[$key] ?? null;