title: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference error while calling an api through retrofit
body: <p>this is my api call where the error is occuring</p>
  
  <pre><code>public void loadData(){
      pd=new ProgressDialog(this);
      pd.setMessage("loading");
      pd.show();
      mApi= new RetrofitHelper&lt;AuthApi&gt;().getApi(AuthApi.class);
      mCall=mApi.studentlist(pageNo);
      mCall.enqueue(new Callback&lt;ResultObject&lt;ArrayList&lt;Person&gt;&gt;&gt;() {
          @Override
          public void onResponse(Call&lt;ResultObject&lt;ArrayList&lt;Person&gt;&gt;&gt; call, Response&lt;ResultObject&lt;ArrayList&lt;Person&gt;&gt;&gt; response) {
              for(int i=0;i&lt;response.body().getData().size();i++){
                  mData.add(response.body().getData().get(i));
              }
              count=response.body().getCount();
              mAdapter=new PersonAdapter(Members.this,R.layout.item_person,mData);
              list.setAdapter(mAdapter);
              pd.hide();
          }
  
          @Override
          public void onFailure(Call&lt;ResultObject&lt;ArrayList&lt;Person&gt;&gt;&gt; call, Throwable t) {
              Toast.makeText(Members.this,"failed",Toast.LENGTH_SHORT).show();
              pd.hide();
          }
      });
  
  
   }
  </code></pre>
  
  <p>this is my logcat while caaling an api,as u can see that i get the response correctly and i at the backend traceball and it is fine with no errors </p>
  
  <pre><code>    07-01 12:23:56.180 12981-13143/com.example.kethan.project D/OkHttp: --&gt; GET http://192.168.0.107:8000/students/?page=1 http/1.1
  07-01 12:23:56.180 12981-13143/com.example.kethan.project D/OkHttp: --&gt; END GET
  07-01 12:23:56.183 12981-12981/com.example.kethan.project D/ActivityThreadInjector: clearCachedDrawables.
  07-01 12:23:56.261 12981-13143/com.example.kethan.project D/OkHttp: &lt;-- 200 OK http://192.168.0.107:8000/students/?page=1 (80ms)
  07-01 12:23:56.261 12981-13143/com.example.kethan.project D/OkHttp: Date: Sat, 01 Jul 2017 06:53:53 GMT
  07-01 12:23:56.261 12981-13143/com.example.kethan.project D/OkHttp: Server: WSGIServer/0.2 CPython/3.5.2
  07-01 12:23:56.261 12981-13143/com.example.kethan.project D/OkHttp: Content-Length: 849
  07-01 12:23:56.261 12981-13143/com.example.kethan.project D/OkHttp: Vary: Accept, Cookie
  07-01 12:23:56.261 12981-13143/com.example.kethan.project D/OkHttp: Content-Type: application/json
  07-01 12:23:56.261 12981-13143/com.example.kethan.project D/OkHttp: X-Frame-Options: SAMEORIGIN
  07-01 12:23:56.262 12981-13143/com.example.kethan.project D/OkHttp: Allow: GET, POST, HEAD, OPTIONS
  07-01 12:23:56.263 12981-13143/com.example.kethan.project D/OkHttp: {"count":37,"next":"http://192.168.0.107:8000/students/?page=2","previous":null,"results":[{"id":35,"name":"kethan","mobile":"8142142827","time":"10:5:0","late":"late by: 5mins 0secs","date":"2017/6/16"},{"id":36,"name":"kethan","mobile":"8142142827","time":"23:28:0","late":"late by: 13hrs 28mins 0secs","date":"2017/06/29"},{"id":37,"name":"kethan","mobile":"8142142827","time":"134","late":"123","date":"123"},{"id":38,"name":"kethan","mobile":"8142142827","time":"134","late":"123","date":"123"},{"id":39,"name":"kethan","mobile":"8142142827","time":"134","late":"123","date":"123"},{"id":40,"name":"kethan","mobile":"8142142827","time":"134","late":"123","date":"123"},{"id":41,"name":"kethan","mobile":"8142142827","time":"134","late":"123","date":"123"},{"id":42,"name":"kethan","mobile":"8142142827","time":"134","late":"123","date":"123"}]}
  07-01 12:23:56.263 12981-13143/com.example.kethan.project D/OkHttp: &lt;-- END HTTP (849-byte body)
  07-01 12:23:56.292 12981-12981/com.example.kethan.project D/AndroidRuntime: Shutting down VM
  
  
                                                                              --------- beginning of crash
  07-01 12:23:56.292 12981-12981/com.example.kethan.project E/AndroidRuntime: FATAL EXCEPTION: main
                                                                              Process: com.example.kethan.project, PID: 12981
                                                                              java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference
                                                                                  at com.example.kethan.project.Members$2.onResponse(Members.java:108)
                                                                                  at retrofit2.ExecutorCallAdapterFactory$ExecutorCallbackCall$1$1.run(ExecutorCallAdapterFactory.java:70)
                                                                                  at android.os.Handler.handleCallback(Handler.java:739)
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                  at android.os.Looper.loop(Looper.java:148)
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:5441)
                                                                                  at java.lang.reflect.Method.invoke(Native Method)
                                                                                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
                                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)
  </code></pre>
  
  <p>this is the result object</p>
  
  <pre><code>public class ResultObject&lt;T&gt; {
  
  private int count;
  
  private T data;
  
  public int getCount() {
      return count;
  }
  
  public T getData() {
      return data;
  }
  
  public void setCount(int count) {
      this.count = count;
  }
  
  public void setData(T data) {
      this.data = data;
  }
  }
  </code></pre>
  
  <p>this is the Person pojo class</p>
  
  <pre><code>public class Person {
  
  private int id;
  
  private String time;
  
  private String late;
  
  private String date;
  
  private String name;
  
  private String mobile;
  
  public String getDate() {
      return date;
  }
  
  public int getId() {
      return id;
  }
  
  public String getTime() {
      return time;
  }
  
  public void setTime(String time) {
      this.time = time;
  }
  
  public String getLate() {
      return late;
  }
  
  public void setLate(String late) {
      this.late = late;
  }
  
  public String getName() {
      return name;
  }
  
  public void setName(String name) {
      this.name = name;
  }
  
  public String getMobile() {
      return mobile;
  }
  
  public void setMobile(String mobile) {
      this.mobile = mobile;
  }
  
  public void setDate(String date) {
      this.date = date;
  }
  
  public void setId(int id) {
      this.id = id;
  }
  }
  </code></pre>