code: public function has($sourceName, $currencyCode, \DateTime $date = null, $rateType = RateType::MEDIAN)
      {
          if ($date === null) {
              $date = new \DateTime('now');
          }
  
          return array_key_exists($this->getRateKey($currencyCode, $date, $rateType, $sourceName), $this->rates);
      }
docs: {@inheritdoc}