Issue with negative button

gistfile1.java

        new MaterialDialog.Builder(this)
                .title(R.string.states)
                .items(R.array.states)
                .itemsCallback(new MaterialDialog.ListCallback() {
                    @Override
                    public void onSelection(MaterialDialog dialog, View view, int which, String text) {
                        Toast.makeText(getApplicationContext(), which + ": " + text, Toast.LENGTH_SHORT).show();
                    }
                })
                .negativeText("Negative")
//                .positiveText("Positive")
                .build()
                .show();