백신 접종 여부 코드

function claimCredential(address _vaccineAddress, uint8 _vaccineType, string calldata _value) public returns(bool){
        require(Credential storage credential = credentials[_vaccineAddress]);
        require(credentials[_vaccineAddress].id == 0);
        credential.id = idCount;
        credential.issuer = msg.sender;
        credential.vaccineType = _vaccineType;
        credential.value = _value;
        credential.createDate = block.timestamp;
  		credential.status = true;

        idCount+=1;

        return true;
}

function isCredential(address _vaccineAddress) public view returns (bool){
         if(credentials[_vaccineAddress].status === true) return true;
         else return false;
}

function VaccineType(uint8 _type, string calldata _value) onlyIssuer public returns (bool) {
        require(bytes(vaccineEnum[_type]).length == 0);
        vaccineEnum[_type] = _value;
        return true;
}