protected function validateConfig(array $config)
    {
        // For now it's only required to pass a filter form type class.
        // If you don't want to use a defined form type class,
        // you can override the FormCreator object, implement FormCreatorInterface and customize it.
        $requiredKeys = ['form_filter_type_class'];

        foreach ($requiredKeys as $key) {
            if (!array_key_exists($key, $config)) {
                throw new FormCreatorException(sprintf(
                    'Key "%s" must be presented in the filters configuration.', $key
                ));
            }

            if (!class_exists($config[$key])) {
                throw new FormCreatorException(sprintf('Class "%s" is not found.', $config[$key]));
            }
        }
    }