Android : NullPointerException : Attempt to read from field 'com.android.volley.Cache$Entry com.android.volley.Response.cacheEntry

Am getting JSONArray from external API using Android Volley. My code is below

StringRequest jq = new StringRequest("http://api.example.com/json/States", new Response.Listener<String>() {

        @Override
        public void onResponse(String jsonArray) {
            try {
                Log.d("Success", jsonArray.toString());
            } catch (Exception je) {
                je.printStackTrace();
            }
        }

    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError volleyError) {
            Log.d("Error", volleyError.toString());
        }
    }) {
        @Override
        protected Response parseNetworkResponse(NetworkResponse networkResponse) {
            return null;
        }
    };
    AppController a = AppController.getInstance();
    Log.d("Queue", "Add");
    a.addToRequestQueue(jq);

Am keep getting same error below

NetworkDispatcher.run: Unhandled exception java.lang.NullPointerException: Attempt to read from field 'com.android.volley.Cache$Entry com.android.volley.Response.cacheEntry' on a null object reference java.lang.NullPointerException: Attempt to read from field 'com.android.volley.Cache$Entry com.android.volley.Response.cacheEntry' on a null object reference at com.android.volley.NetworkDispatcher.run(NetworkDispatcher.java:126)

I tried various methods. But still am having same problem. I Cant understand where is the issue. Help to fix this