HTTPS with Poco: Certificate verify failed

I'm trying to get HTTPS running using the POCO library using this little program:

int main()
{
    // For debugging purposes to inspect verification errors.
    SharedPtr<InvalidCertHandler> invalidCertHandler(new InvalidCertHandler());

    URI uri("https://google.com/");

    Context::Ptr ctx = new Context(Context::CLIENT_USE, "", Context::VerificationMode::VERIFY_RELAXED, 9, true);
    SSLManager::instance().initializeClient(nullptr, invalidCertHandler, ctx);
    HTTPSClientSession httpSession(uri.getHost(), uri.getPort(), ctx);
    HTTPRequest request(HTTPRequest::HTTP_GET, uri.getPath(), HTTPRequest::HTTP_1_1);
    HTTPResponse response;

    try
    {
        httpSession.sendRequest(request);
        httpSession.receiveResponse(response);
    }
    catch (Exception ex)
    {
        cout << ex.message() << endl;
        return -1;
    }

    cout << "Success" << endl;
    return 0;
}

Unfortunately I always get the following exception message when running the program:

error:14090086:SSL routines:ssl3_get_server_certificate:certificate verify failed

And the following message in my InvalidCertHandler:

unable to get local issuer certificate

After that I opened https://google.com/in Google Chrome and exported the certificate in Base64-encoded X.509 Format (.CER) and initialized the Context with the absolute path of the .cer file instead of just an empty string. That didn't work too.

I don't know what I'm doing wrong here but I would like to know.
Can anyone of you help me out on this?