Cascade detectMultiScale shows error while running

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try {
    auto axes = CvPlot::plotImage(clone);
    cv::Mat mat = axes.render(clone.size().width, clone.size().height);
    CvPlot::show(title, axes);
    waitKey(0);
}
catch (cv::Exception& e)
{
    std::cerr << e.msg << std::endl;
}