I am getting the error

```
ActionView::Template::Error (undefined method `values_at' for nil:NilClass):

```

when using nested\_form gem 

Here is my code

Models

```
class Poll < ActiveRecord::Base

  attr_accessible :question, :poll_answers_attributes
  has_many  :poll_answers
  accepts_nested_attributes_for :poll_answers
end

class PollAnswer < ActiveRecord::Base
  belongs_to  :poll
  attr_accessible :answer
end

```

View 

```
 =nested_form_for [:admin, @poll], mutipart: true, class: "form-horizontal" do |f|
    .span6
      .control-group
        =f.label :question, class: "control-label"
        .controls
          =f.text_field :question, rows: "5", class: "span5"
      = f.link_to_add "Add a Answer", :poll_answers
      =f.submit "Create Post", class: "btn btn-primary"

```

StackTrace

```
/home/abid/.bundler/ruby/1.9.1/nested_form-6232dd853c27/lib/nested_form/builder_mixin.rb:41:in `block in link_to_add'
/home/abid/.bundler/ruby/1.9.1/nested_form-6232dd853c27/lib/nested_form/view_helper.rb:53:in `call'
/home/abid/.bundler/ruby/1.9.1/nested_form-6232dd853c27/lib/nested_form/view_helper.rb:53:in `after_nested_form_callbacks'
/home/abid/.bundler/ruby/1.9.1/nested_form-6232dd853c27/lib/nested_form/view_helper.rb:8:in `block in nested_form_for'

```

Any Ideas ?