title: date_field - can't convert Symbol into String
body: <p>I'm quite fresh ruby on rails developer and i'm experiencing some troubles with displaying <code>date_field</code> in user profile edit form. It suddenly stopped working and i can't debug what's wrong and why it's not working. Here is my code:</p>
  
  <p><strong>_form.html.haml</strong></p>
  
  <pre><code>= form_for(@profile) do |f|
    = f.label :dob, 'Date of birth', :class =&gt; 'control-label'
    = f.date_select :dob, :start_year =&gt; Time.now.year - 50, :end_year =&gt; Time.now.year - 5, :include_blank =&gt; true
  </code></pre>
  
  <p>It gives me the following error:</p>
  
  <blockquote>
    <p>can't convert Symbol into String</p>
  </blockquote>
  
  <p>on line 26 which is the one with <code>date_select</code>. I'm getting this error no matter if <code>dob</code> field is empty or not. Have you any idea what am i possibly missing? The strange thing is that it was working yesterday.</p>