Error on 3D IsoSurfaces

Im trying to do isosurfaces on 3d data; im following the examples in
test01 and test59;
i get the following VisAD Exception:

java.lang.NullPointerException
        at visad.Irregular3DSet.makeSpatial(Irregular3DSet.java:179)
        at visad.ShadowType.assembleSpatial(ShadowType.java:1678)
        at
visad.ShadowFunctionOrSetType.doTransform(ShadowFunctionOrSetType.java:1
605)
        at
visad.java3d.ShadowFunctionOrSetTypeJ3D.doTransform(ShadowFunctionOrSetT
ypeJ3D.java:102)
        at
visad.java3d.DefaultRendererJ3D.doTransform(DefaultRendererJ3D.java:86)
        at visad.java3d.RendererJ3D.doAction(RendererJ3D.java:180)
        at visad.DisplayImpl.doAction(DisplayImpl.java:852)
        at visad.ActionImpl.run(ActionImpl.java:186)
        at visad.util.ThreadPool$ThreadMinnow.run(ThreadPool.java:86)

here's the jist of the code:

    int sizeX = xaxis.getNumElements();
    int sizeY = yaxis.getNumElements();
    int sizeZ = zaxis.getNumElements();

    int[] index = {0, 0, 0};
    float[][] xyz = new float[3][(int) arr.getSize()];
    float[][] f = new float[1][(int) arr.getSize()];

    long startTime = System.currentTimeMillis();
    for (int k=0; k<sizeZ; k++) {
     for (int j=0; j<sizeY; j++) {
      for (int i=0; i<sizeX; i++) {
        int elem = i + (j + k*sizeY)*sizeX;
        index[0] = k;
        index[1] = j;
        index[2] = i;
        f[0][elem] = arr.getFloat(index);

        xyz[0][elem] = (float) xaxis.getCoordValue(i);
        xyz[1][elem] = (float) yaxis.getCoordValue(j);
        xyz[2][elem] = (float) zaxis.getCoordValue(k);
      }
     }
    }

    RealType xtype = VisUtil.RealTypeFactory(xname);
    RealType ytype = VisUtil.RealTypeFactory(yname);
    RealType ztype = VisUtil.RealTypeFactory(zname);
    RealType ftype = VisUtil.RealTypeFactory(fname);

    RealTupleType xyzType = new RealTupleType(xtype, ytype, ztype);
    FunctionType ft = new FunctionType(xyzType, ftype);

    Gridded3DSet xyzSet = new Gridded3DSet(xyzType, xyz, nx, ny, nz);
    FlatField ffld = new FlatField(ft, xyzSet);
    ffld.setSamples(f);

    // create a DataReference
    DataReference setRef = new DataReferenceImpl("Visad_DataReference");
    setRef.setData(ffld);

    // create a Display using Java3D
    DisplayImpl display = new DisplayImplJ3D("Visad3D_Display");

    // map plot to display coordinates
    display.addMap(new ScalarMap(xtype, Display.XAxis));
    display.addMap(new ScalarMap(ytype, Display.YAxis));
    display.addMap(new ScalarMap(ytype, Display.ZAxis));

    display.addMap(new ScalarMap(ftype, Display.IsoContour));


    // link the Display to the data
    display.addReference(setRef);

    // add axes
    GraphicsModeControl mode = display.getGraphicsModeControl();
    mode.setScaleEnable(true);

    // return a JComponent of preferred size
    JComponent c = (JComponent) display.getComponent();
    c.setPreferredSize(displaySize);
    return c;