title: Icinga2 object ApiUser is unknown
body: <p>I need help understanding an error why I'm seeing an error. 
  The feature <code>api</code> is already enabled with the correct ApiListener object, and Api logs are being updated in <code>/var/lib/icinga2/api/log/current</code> .</p>
  
  <p>But I'm getting this error when I restart icinga2:</p>
  
  <pre><code>Error: Error while evaluating expression: The type 'ApiUser' is unknown: in /etc/icinga2/conf.d/api-users.conf: 1:0-1:20
  </code></pre>
  
  <p>I'm running version r2.3.10-1 of Icinga2 on Ubuntu.</p>
  
  <p>Can someone explain what the problem is?</p>