Decide the clickable status of check box according to json response

I have a check box in my application and it should be clickable when mayoBase returns true and its shouldn't be clickable when mayoBase returns false. I have tried the below mentioned code, but it crashes. I have attached my logcat, how can I overcome this. Any help will be appreciated.

@Override
    public void onTaskCompleted(JSONArray responseJson) {

        try {
            List<String> mayoBase = new ArrayList<String>();

            for (int i = 0; i < responseJson.length(); ++i) {
                JSONObject object = responseJson.getJSONObject(i);

                if ((object.getString("MainCategoryID")).equals("1")) {
                    Log.i("Description ", object.getString("Description"));
                    descriptionHalf.add(object.getString("Description"));

                    Log.i("IsMayoBaseAvailable", object.getString("IsMayoBaseAvailable"));
                    mayoBase.add(object.getString("IsMayoBaseAvailable"));

                }

                String strIsVag = mayoBase.get(i); //line 392
            mayoBaseCB = (CheckBox) findViewById(R.id.ch_mayobase);
            if (strIsVag.contains("true")) {
                mayoBaseCB.setEnabled(true);
            } else {
                mayoBaseCB.setEnabled(false);
            }