/**
  * @param ConfigInterface $config
  *
  * @return DirectiveInterface
  * @throws Exception
  */
 public function mergeInto(ConfigInterface $config) : DirectiveInterface
 {
     $identifier = static::class;
     $currentValue = $this->mergePolicy ? [] : $config->get($identifier, []);
     $currentValue[] = $this->value;
     $config->set($identifier, $currentValue);
     return $this;
 }