Setono / TinyPngBundle

DependencyInjection/Configuration.php

<?php

declare(strict_types=1);

namespace Setono\TinyPngBundle\DependencyInjection;

use Symfony\Component\Config\Definition\Builder\TreeBuilder;
use Symfony\Component\Config\Definition\ConfigurationInterface;

final class Configuration implements ConfigurationInterface
{
    /**
     * {@inheritdoc}
     */
    public function getConfigTreeBuilder(): TreeBuilder
    {
        $treeBuilder = new TreeBuilder();
        $rootNode = $treeBuilder->root('setono_tiny_png');
        $rootNode
            ->addDefaultsIfNotSet()

The method addDefaultsIfNotSet() does not exist on Symfony\Component\Config\Definition\Builder\NodeDefinition. It seems like you code against a sub-type of Symfony\Component\Config\Definition\Builder\NodeDefinition such as Symfony\Component\Config\Definition\Builder\ArrayNodeDefinition.

            ->children()
                ->scalarNode('api_key')
                    ->isRequired()
                    ->cannotBeEmpty()
                    ->info('Your TinyPNG API key')
                ->end()
                ->scalarNode('proxy')
                    ->defaultNull()
                    ->cannotBeEmpty()
                    ->info('The proxy to use')
                ->end()
            ->end()
        ;

        return $treeBuilder;
    }
}