title: AssetTagHelper::image_path outside views
body: <p>Supposedly, <code>ActionController::Base.helpers</code> acts like a proxy for accessing helpers outside views. However many of the methods defined there rely on controller variables and I'm unable to succesfully call:</p>
  
  <pre><code>ActionController::Base.helpers.image_path("my_image.png")
  &gt;&gt; TypeError Exception: can't convert nil into String
  </code></pre>
  
  <p>Digging at the source I see <code>compute_asset_host</code> method is trying to access <code>config.asset_host</code> but <code>config</code> is <code>nil</code>.</p>
  
  <p>How can I successfully call <code>image_path</code> from outside views?</p>