public function createCore()
    {
        $config = new MemoryConfigCollection();

        // Set default middleware
        $config->setMiddlewares([
            new InheritanceMiddleware(Config::UNINHERITED),
            new ExtensionMiddleware(Config::EXCLUDE_EXTRA_SOURCES),
        ]);

        // Transform
        $config->transform([
            $this->buildStaticTransformer(),
            $this->buildYamlTransformer()
        ]);

        return $config;
    }