fix(typing): wrong return type

Author: vinceAmstoutz

core/dto.md

@@ -272,7 +272,8 @@ final class BookProvider implements ProviderInterface
         private readonly ProviderInterface $collectionProvider,
     ) {}
 
-    public function provide(Operation $operation, array $uriVariables = [], array $context = []): ?PostalAddress
+    /** @return array<Book> */
+    public function provide(Operation $operation, array $uriVariables = [], array $context = []): array
     {
         $resources = $this->collectionProvider->provide($operation, $uriVariables, $context);