List View problem

I cannot figure out why it's throwing a NullPointerExce开发者_开发知识库ption on line 28, which is return mClasses.size(); and I cant figure out why, Any Ideas?

private ArrayList<String> mClasses;
    public int size;
    public mAdapter(Context context,ArrayList<String> classes,ArrayList<Integer> checked) {
        mInflater = LayoutInflater.from(context);
        mClasses = classes;
        mChecked = checked;
    }

    public int getCount() {
        return mClasses.size();
    }
..etc
}

My guess is the "classes" your a passing is null. easily checkable with a

if(calsses == null)Log.e("error","parameter classes is null);

or launch in debug add a break point on your return and look at the values of the parameters around the breakpoint.

return this.size();

I think.