title: accepts_nested_attributes_for stops my sub-form rendering?
body: <p>I have an association between 2 models, Business and Address. where the business has a registered_address. I have done this as follows.</p>
  
  <pre><code>class Business &lt; ActiveRecord::Base  
      has_one :registered_address, :class_name =&gt; "Address", :foreign_key =&gt; :business_registered_address_id
      accepts_nested_attributes_for :registered_address
  end
  
  class Address &lt; ActiveRecord::Base
      belongs_to :business
  end
  </code></pre>
  
  <p>This association works fine for my purposes. When I render the form using:</p>
  
  <pre><code>= form_for @business do |form|
    = form.inputs :name =&gt; "Registered address" do
      = form.fields_for :registered_address do |address|
        = address.input :postcode
        = address.input :line_1
        = address.input :line_2
        = address.input :line_3
        = address.input :town
        = address.input :county
  </code></pre>
  
  <p>Nothing is displayed, just an empty fieldset. </p>
  
  <p>When I comment out the accepts_nested_attributes_for line in Business model, it displays (but doesn't save) all the fields correctly.</p>
  
  <p>Can anyone see what I'm doing wrong?</p>
  
  <p>Thank you</p>