title: Filtering using collection_select params
body: <p>I have simple form which allows users to filter search results according to <code>location_id</code> which is given in  <code>collection_select</code> form's field. I want to render narrowed results if  specific location is selected, and render all results if user selects default "Please select" field.</p>
  
  <p>This code works good for separate locations, but not working if user selects "please select" field. <code>params[:location_id].blank?</code> in controller not working.</p>
  
  <p>view</p>
  
  <pre><code>&lt;%= form_tag @city %&gt;
    &lt;%= collection_select 'location_id', nil, @city.locations, :id, :address, prompt: true %&gt;
    &lt;%= submit_tag "sort", :name =&gt; nil, class: "btn btn-success travel-button", id: "hotels-radius-search-button" %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>controller</p>
  
  <pre><code>if params[:location_id].blank?
    ...render all results...
  else
    ..render specific results...
  end
  </code></pre>
  
  <p><strong>Update</strong></p>
  
  <p>Server's response</p>
  
  <p>Parameters when default "Please select" option is selected -- not working</p>
  
  <pre><code>Parameters: {"utf8"=&gt;"✓", "search_radius"=&gt;"6", "location_id"=&gt;[""], "_"=&gt;"1365350127863", "id"=&gt;"75"}
  </code></pre>
  
  <p>Parameters when user select any option in menu -- succesful</p>
  
  <pre><code>Parameters: {"utf8"=&gt;"✓", "search_radius"=&gt;"6", "location_id"=&gt;["811"], "_"=&gt;"1365350127865", "id"=&gt;"75"}
  </code></pre>
  
  <p>or</p>
  
  <pre><code>Parameters: {"utf8"=&gt;"✓", "search_radius"=&gt;"6", "location_id"=&gt;["808"], "_"=&gt;"1365350127865", "id"=&gt;"75"}
  </code></pre>
  
  <p>etc</p>