title: text_field disabled in Ruby on Rails
body: <p>I have the following code to disable a <code>text_field</code> when a user is not an admin and it is working fine:</p>
  
  <pre><code>&lt;div class="form-group"&gt;
  &lt;%= f.label :nome, "Genero" %&gt;
  &lt;%= f.text_field :nome, class: "form-control", disabled: true if not is_admin? %&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>But when a user is an admin the <code>text_field</code> just disappears.  Does anyone know why this is happening and what I have to do?</p>