title: Object reference not set to an instance of an object
body: <p>I usually get this error and (always) don't know how to solve it.
  This time I got it also, it seems that I'm not understanding a concept or missing something
  Here's the code</p>
  
  <pre><code>        // create a new twitteroo core with provided username/password
          TwitterooCore core = new TwitterooCore(username, password);
  
          // request friends timeline from twitter
          Users users = core.GetTimeline(Timeline.Friends); // error here
  </code></pre>
  
  <p>Please some help and also some explanations of what's happening
  Thanks</p>