gc.getSampleDimension(0).getMinimumValue() seems not working properly

Hello,
I am trying to get the "minimum" and "no data value" from my GridCoverage created from AsciiArcGrid but it return the no data value (-9999) for the minimum and "null" for the no data value instead of the actual minimum value and no data value(-9999) respectively.

Herebelow is the way I do it.

URL arcURL=f.toURI().toURL();
ArcGridReader gridreader = new ArcGridReader(arcURL);
GridCoverage2D gc2 = (GridCoverage2D)gridreader.read(null);

....gc2.getSampleDimension(0).getNoDataValues();
...gc2.getSampleDimension(0).getMinimumValue();

I would appreciate if anybody can help.
Thanks.