code: public function has($sourceName, $currencyCode, \DateTime $date = null, $rateType = RateType::MEDIAN)
      {
          if ($date === null) {
              $date = new \DateTime('now');
          }
  
          try {
              return (bool)$this->get($sourceName, $currencyCode, $date, $rateType);
          } catch (ExchangeRateException $e) {
              return false;
          }
      }
docs: {@inheritdoc}