title: I get a "NullPointerException" when I'm trying to implement ListView Volley
body: <p>I've tried to do <strong>everything</strong> as in <a href="http://www.androidhive.info/2014/07/android-custom-listview-with-image-and-text-using-volley/" rel="nofollow">this</a> tutorial: 
  but I don't know what is the problem there. </p>
  
  <pre><code>     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.app.ActionBar.setBackgroundDrawable(android.graphics.drawable.Drawable)' on a null object reference
              at info.androidhive.customlistviewvolley.MainActivity.onCreate(MainActivity.java:55)
              at android.app.Activity.performCreate(Activity.java:6185)
  </code></pre>