title: Received null in Response when using volley to send ArryList to server
body: <p>I tried send an arraylist to server by volley,but I received null in my response method
  I make ArrayList with this code:</p>
  
  <pre><code>final ArrayList&lt;HashMap&lt;String, String&gt;&gt; arrayList = new ArrayList&lt;HashMap&lt;String, String&gt;&gt;();
  
          for (int i = 0; i &lt; questions.size(); i++) {
  
              //addToServer(questions.get(i),questions.size());
  
              HashMap&lt;String, String&gt; params = new HashMap&lt;String, String&gt;();
              params.put("TestId", questions.get(i).getTestId() + "");
              params.put("Number", questions.get(i).getNumber() + "");
  
              arrayList.add(params);
               }
  
          listOfQ = new JSONArray(arrayList);
  </code></pre>
  
  <p>and send It to server by this code :</p>
  
  <pre><code>public void addToServer2() {
  
      if(requestQueue == null){
          requestQueue = Volley.newRequestQueue(myContext);
  
      }
      request = new StringRequest(Request.Method.POST, ServiceApi.URL_send_question2, new Response.Listener&lt;String&gt;() {
          @Override
          public void onResponse(String response) {
              try {
                  JSONArray jsonArray = new JSONArray(response);
              } catch (JSONException e) {
                  e.printStackTrace();
              } catch (Exception e) {
              }
          }
      }, new Response.ErrorListener() {
          @Override
          public void onErrorResponse(VolleyError error) {
  
          }
      }) {
          @Override
          protected Map&lt;String, String&gt; getParams() throws AuthFailureError {
  
              Map&lt;String, String&gt; params = new HashMap&lt;String, String&gt;();
  
              params.put("test", listOfQ.toString());
              return params;
          }
  
          @Override
          public Map&lt;String, String&gt; getHeaders() throws AuthFailureError {
              return super.getHeaders();
          }
      };
  
      requestQueue.add(request);
  }
  </code></pre>
  
  <p>and here is my php code that get arraylist and back one value to android side:</p>
  
  <pre><code>$arr = array();
  $jsonarray = array();
  
  
  $json = $_POST['test'];
  $jsonarray = json_decode($json,true);
  
  foreach((array) $jsonarray as $key){
  
       $TestId = $key["TestId"];
       $arr[] = array('id' =&gt; $TestId);
   }
  </code></pre>
  
  <p>when i debug my application it show me this in response : id:null</p>