title: Rails 4 Make Default for f select null
body: <p>I want to make the default option for my dropdown select in a form null. I added</p>
  
  <pre><code>{:include_blank =&gt; true}
  </code></pre>
  
  <p>but the initial blank option is not showing up.</p>
  
  <p>Here's the line of code:</p>
  
  <pre><code>&lt;%= f.select :user_ids, options_for_select(User.all.collect{|user| [user.name, user.id]}, @reservation.user_ids), {multiple: true, :class=&gt;'user-id-widget', size: 5}, {:include_blank =&gt; true} %&gt;
  </code></pre>