public function getSurveyDownloadCodesUrl(): ?string 	{ 		switch ($this->survey_type) { 			case SurveyType::PULS: 				$url_name = 'api.client-surveys-puls.email-pdf-codes';  				break;  			default: 				$url_name = 'api.client-surveys.email-pdf-codes';  				break; 		}  		$expiration = $this->end_date; 		$parameters = ['id' => $this->getKey()];  		return $this->applicants()->fillingOnlineSurvey()->whereNull('email')->exists() ? URL::temporarySignedRoute($url_name, $expiration, $parameters) : null; 	}