title: XtifySDK.getXidKey() returns null
body: <p>I'm following the instructions as the Getting Started section for Xtify notifications doing the following:</p>
  
  <pre><code>Context myAppContext = getApplicationContext();
  
  XtifySDK.start(myAppContext , MyApp.XTIFY_APP_KEY, MyApp.SENDER_ID);
  String xid = XtifySDK.getXidKey(myAppContext);
  
  if(!"".equals(xid) &amp;&amp; xid != null) {
  ...
  }
  </code></pre>
  
  <p>And I realised that when I register for the first time, it returned the Xid, but if I uninstall and deploy again using Eclipse It returns null in <code>XtifySDK.getXidKey()</code> instruction.</p>
  
  <p>The app target is build using Google APIs 4.0 (level 14).</p>
  
  <p>I'd thank and appreciate your help in this guys.</p>