title: Activeadmin : undefined method `access_denied'
body: <p>I use rails 5.0
  cancan 1.6.10
  devise 4.2.0
  Activeadmin </p>
  
  <p>I regulary have this error in newrelic : </p>
  
  <pre><code>NoMethodError: undefined method `access_denied' for #&lt;Admin::FollowupsController:0x007f112917d270&gt;
  </code></pre>
  
  <p>In active_admin.rb i set :access_denied in the config : </p>
  
  <pre><code>  config.on_unauthorized_access = :access_denied
  </code></pre>
  
  <p>How can I remove this error and have a good management of redirection for access_denied instead of a 500 ? </p>