title: Missing partial in Rails 4 project
body: <p>in my simple project I decide to use nested form and using for it cocoon gem. but after implementing it I get Missing partial error, although I have partial file with underline. this is my cocoon logic code:</p>
  
  <p><strong>_form.html.erb</strong></p>
  
  <pre><code>... form_for starts...
  
  &lt;div class="row"&gt;
      &lt;div class="col-md-6"&gt;
        &lt;h3&gt;Ingredients&lt;/h3&gt;
          &lt;%= f.fields_for :ingredients do |ingredient| %&gt;
              &lt;%= render 'ingredients', f: ingredient %&gt;
          &lt;% end %&gt;
          &lt;%= link_to_add_association "Add", f, :ingredients %&gt;
      &lt;/div&gt;
    &lt;/div&gt;
  
  ...submit and cancel buttons...
  </code></pre>
  
  <p>this is my partial file <strong>_ingredients.html.erb</strong></p>
  
  <pre><code>&lt;div class="nested-fields"&gt;
    &lt;%= f.label :name %&gt;
    &lt;%= f.text_field :name %&gt;
  
    &lt;%= f.label :count %&gt;
    &lt;%= f.text_field :count %&gt;
  
    &lt;%= f.label :description %&gt;
    &lt;%= f.text_field :description %&gt;
    &lt;%= link_to_remove_association "Remove", f %&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/SGOOe.png" alt="enter image description here"></p>