title: NullPointerException addToRequestQueue(com.android.volley.Request, java.lang.String)' on a null object reference
body: <p>I'm using <a href="http://www.androidhive.info/2012/01/android-login-and-registration-with-php-mysql-and-sqlite/" rel="noreferrer">AndroidHive register login</a> and it's working fine in example project of this login-register.</p>
  
  <p>But after many attempts trying it with <code>CardView</code>s and other widgets, this error appears on the <code>LogCat</code>:</p>
  
  <pre><code>java.lang.NullPointerException: Attempt to invoke virtual method 'void client.myproject.app.AppController.addToRequestQueue(com.android.volley.Request, java.lang.String)' on a null object reference
              at client.myproject.RegisterActivity.registerUser(RegisterActivity.java:185)
              at client.myproject.RegisterActivity.access$300(RegisterActivity.java:35)
              at client.myproject.RegisterActivity$1.onClick(RegisterActivity.java:81)
              at android.view.View.performClick(View.java:4780)
              at android.view.View$PerformClick.run(View.java:19866)
              at android.os.Handler.handleCallback(Handler.java:739)
              at android.os.Handler.dispatchMessage(Handler.java:95)
              at android.os.Looper.loop(Looper.java:135)
              at android.app.ActivityThread.main(ActivityThread.java:5254)
              at java.lang.reflect.Method.invoke(Native Method)
              at java.lang.reflect.Method.invoke(Method.java:372)
              at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
  </code></pre>
  
  <p>While these codes works fine in a single app (just with register login).</p>
  
  <p>I'm using Volley library. </p>