title: Form_tag url_for_options nil action to the controller itself
body: <p>My case is that i have more controllers with sharing one view and i'm trying to change dinamycally the action on a form passing a variable defined in the controller</p>
  
  <p>Trying some solution i've observed that if i have a nil variable in url_for_options form_tab variable, the form in the view has the right controller path from where the view was called</p>
  
  <p><code>
  &lt;%= form_tag nil, :method =&gt; :get, :class =&gt; 'search' do %&gt;
  </code></p>
  
  <p>is it a bug or a feature?</p>