When using EnumNode with a BackedEnum (via enumFqcn) and explicitly allowing null values (e.g. ->defaultNull()), the finalization logic incorrectly throws an InvalidConfigurationException:

"Only strings and integers can be cast to a case of the "Symfony\Component\Config\Tests\Fixtures\StringBackedTestEnum" enum, got value of type "null""

$rootNode
    ->children()
        ->enumNode('status')
            ->enumFqcn(StringBackedTestEnum::class)
            ->defaultNull() // Now correctly allows null in config
        ->end()
    ->end()
;