title: rails simple_nested_form_for fields_for wrong number of arguments
body: <p>So I'm building a form in rails 3.1, using </p>
  
  <pre><code>&lt;%= simple_nested_form_for(@person, :url =&gt; collection_url, :html=&gt;{:multipart =&gt; true}) do |f| %&gt;
    &lt;%= render :partial =&gt; "form", :locals =&gt; { :f =&gt; f } %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>but this line in the partial is causing the problem:</p>
  
  <pre><code>&lt;h2&gt;Badges&lt;/h2&gt; 
  &lt;ul id="certifications"&gt;
  // this following line is raising the error "wrong number of arguments (4 for 3)"
  &lt;%= f.fields_for :certifications do |certification_form| %&gt; 
      &lt;%= render :partial =&gt; 'certification', :locals =&gt; { :f =&gt; certification_form } %&gt;
  &lt;% end %&gt;
  &lt;/ul&gt;
  &lt;%= f.link_to_add "Add a Badge", :certifications %&gt;
  </code></pre>
  
  <p>So here is the model: </p>
  
  <pre><code>class Person &lt; ActiveRecord::Base
    has_many :certifications, :dependent=&gt;:destroy, :order=&gt;:position
    has_many :certificates, :through=&gt;:certifications
    accepts_nested_attributes_for :certifications, :allow_destroy =&gt; true
  end
  </code></pre>
  
  <p>The controller is using the inherited resource gem. </p>
  
  <p>What's wrong? Thanks for the help. </p>