JAVA-JHepWork数据拟合（curve fitting）报错：“/ is a folder”

import java.awt.Color;
import java.util.*;
import jhplot.*;
import jhplot.stat.LinReg;

public class ScanTest2 {

public static void main(String[] args)
{
    HPlot c1=new HPlot("cad");
    c1.visible();
    c1.setAutoRange();

    HFitter f=new HFitter();
    f.setFunc("g");

    P1D p1=new P1D();
    p1.setPenWidth(2);
    p1.setDrawLine(false);
    p1.setColor(Color.red);
    Random r=new Random();
    for(int i=0;i<=100;i++){
        double x=r.nextGaussian();
        double y=180+30*x;
        p1.add(x, y);
    }
    c1.draw(p1);

    //f.fit(p1);
    //f.fit(p1);

// LinReg lr=new LinReg(p1);
// c1.draw(lr.getResult());
// c1.draw(lr.getPrediction(Color.red));
}

}

错误信息：
Exception in thread "main" java.lang.IllegalArgumentException: / is a folder
at hep.aida.ref.tree.Tree.rm(Tree.java:588)
at hep.aida.ref.tree.Tree.add(Tree.java:1129)
at hep.aida.ref.tree.Tree.add(Tree.java:1115)
at hep.aida.ref.tree.Tree.addFromFactory(Tree.java:1110)
at hep.aida.ref.histogram.DataPointSetFactory.create(DataPointSetFactory.java:55)
at hep.aida.ref.histogram.DataPointSetFactory.create(DataPointSetFactory.java:51)
at jhplot.P1D.getIDataPointSet(P1D.java:4799)
at jhplot.HFitter.doFit(HFitter.java:430)
at jhplot.HFitter.fit(HFitter.java:334)
at com.sbl.io.video.ScanTest2.main(ScanTest2.java:36)