title: Tiki: Unexpected return from trackerlib -> get_item_creators
body: <p>I upgraded my tiki from 15.4 to 16.2. Everything runs fine. The problem is the site registration does not work. I have a tracker to extend my user information. In the tracker, I created a field called "Network" that allows the users to choose a group that them want to be in. Hence, they won't see each other content due to different group permission. This registration broke. The error message showed: </p>
  
  <blockquote>
    <p>Cannot add nonexistent user xxx to group students</p>
  </blockquote>
  
  <p>I found out the problem was that there is a change in trackerlib.php line 3671. Instead of returning "null", it now returns an empty array().</p>
  
  <pre><code>else {
      return array();
  }
  </code></pre>
  
  <p>In GroupSelector.php, line 124, the condition check </p>
  
  <pre><code>if (empty ($creators))) $creators=array($user);
  </code></pre>
  
  <p>This if will never be executed since the function now return an array not null. Hence causing the problem that no one can be registered if they choose a group in the registration form. </p>
  
  <p>Propose solution, change the if condition in line 124 to:</p>
  
  <pre><code>if (empty($creators[0]))
  </code></pre>