Rails no implicit conversion of String into Integer

Someone please could give a hint why show this message

no implicit conversion of String into Integer

when i put this code

<% @products.response["aggregations"]["category"]["buckets"].each do |c| %>
        <li class="list-group-item">
          <%= link_to "#{c['name']} #{c['key']} : #{c['doc_count']}"%>
        </li>
      <% end %> 

on the view?

thank's