DependencyInjection/Configuration.php
public function getConfigTreeBuilder()
    {
        $builder = new TreeBuilder('sb_json_request');

        if (\method_exists($builder, 'getRootNode')) {
            $rootNode = $builder->getRootNode();
        } else {
            // BC layer for symfony/config 4.1 and older
            $rootNode = $builder->root('maker');
        }

        $rootNode
            ->children()
                ->arrayNode('listener')
                    ->addDefaultsIfNotSet()
                    ->children()
                        ->scalarNode('request_transformer')
                            ->defaultValue(RequestTransformerListener::class)
                        ->end()
                        ->scalarNode('priority')
                            ->defaultValue(100)
                        ->end()
                    ->end()
                ->end()
            ->end();

        return $builder;
    }
public function getConfigTreeBuilder()
    {
        $builder = new TreeBuilder('sb_json_request');

        if (\method_exists($builder, 'getRootNode')) {
            $rootNode = $builder->getRootNode();
        } else {
            // BC layer for symfony/config 4.1 and older
            $rootNode = $builder->root('maker');
        }

        $rootNode
            ->children()
                ->arrayNode('listener')
                    ->addDefaultsIfNotSet()
                    ->children()
                        ->scalarNode('request_transformer')
                            ->defaultValue(RequestTransformerListener::class)
                        ->end()
                        ->scalarNode('priority')
                            ->defaultValue(100)
                        ->end()
                    ->end()
                ->end()
            ->end();

        return $builder;
    }
{@inheritdoc}