class Author {
    public $name;
}

class Blog {
    public $title;
    public Author $author;
}

// when there is no issue
$blog = $denormalizer->denormalize([
    'title' => 'test title',
    'author' => [
        'name' => 'test name',
    ],
], Blog::class);


// when a type error is thrown
$blog = $denormalizer->denormalize([
    'title' => 'test title',
    'author' => 'test string',
], Blog::class);

TypeError:
Symfony\Component\Serializer\Normalizer\AbstractNormalizer::prepareForDenormalization(): Argument #1 ($data) must be of type object|array|null, string given, called in /var/www/symfony/vendor/symfony/serializer/Normalizer/AbstractObjectNormalizer.php on line 368

  at vendor/symfony/serializer/Normalizer/AbstractNormalizer.php:299
  at Symfony\Component\Serializer\Normalizer\AbstractNormalizer->prepareForDenormalization('test string')
     (vendor/symfony/serializer/Normalizer/AbstractObjectNormalizer.php:368)
  at Symfony\Component\Serializer\Normalizer\AbstractObjectNormalizer->denormalize('test string', 'App\\Entity\\User', null, array('cache_key' => 'c93a6d4efa206ea58a62cc6b7fab8dfb', 'deserialization_path' => 'author'))
     (vendor/symfony/serializer/Serializer.php:238)
  at Symfony\Component\Serializer\Serializer->denormalize('test string', 'App\\Entity\\User', null, array('cache_key' => 'c93a6d4efa206ea58a62cc6b7fab8dfb', 'deserialization_path' => 'author'))
     (vendor/symfony/serializer/Normalizer/AbstractObjectNormalizer.php:559)
  at Symfony\Component\Serializer\Normalizer\AbstractObjectNormalizer->validateAndDenormalize(array(object(Type)), 'App\\Entity\\Blog', 'author', 'test string', null, array('cache_key' => '44db5a926a1544b1a8585af40107ca3a', 'deserialization_path' => 'author'))
     (vendor/symfony/serializer/Normalizer/AbstractObjectNormalizer.php:401)
  at Symfony\Component\Serializer\Normalizer\AbstractObjectNormalizer->denormalize(array('title' => 'test title', 'author' => 'test string'), 'App\\Entity\\Blog', null, array('cache_key' => '44db5a926a1544b1a8585af40107ca3a'))
     (vendor/symfony/serializer/Serializer.php:238)
  at Symfony\Component\Serializer\Serializer->denormalize(array('title' => 'test title', 'author' => 'test string'), 'App\\Entity\\Blog')
     (src/Controller/BugReproductionController.php:19)
  at App\Controller\BugReproductionController->test(object(Serializer))
     (vendor/symfony/http-kernel/HttpKernel.php:152)
  at Symfony\Component\HttpKernel\HttpKernel->handleRaw(object(Request), 1)
     (vendor/symfony/http-kernel/HttpKernel.php:74)
  at Symfony\Component\HttpKernel\HttpKernel->handle(object(Request), 1, true)
     (vendor/symfony/http-kernel/Kernel.php:202)
  at Symfony\Component\HttpKernel\Kernel->handle(object(Request))
     (vendor/symfony/runtime/Runner/Symfony/HttpKernelRunner.php:35)
  at Symfony\Component\Runtime\Runner\Symfony\HttpKernelRunner->run()
     (vendor/autoload_runtime.php:29)
  at require_once('/var/www/symfony/vendor/autoload_runtime.php')
     (public/index.php:5)         

/**
 * Normalizes the given data to an array. It's particularly useful during
 * the denormalization process.
 */
protected function prepareForDenormalization(object|array|null $data): array
{
    return (array) $data;
}

/**
 * Normalizes the given data to an array. It's particularly useful during
 * the denormalization process.
 */
protected function prepareForDenormalization(mixed $data): array
{
    if (is_scalar($data)) {
        throw new Symfony\Component\Serializer\Exception\UnexpectedValueException();
    }

    return (array) $data;
}