title: rails simple_form - hidden field - create?
body: <p>How can you have a hidden field with simple form?</p>
  
  <p>The following code:</p>
  
  <pre><code>= simple_form_for @movie do |f|
    = f.hidden :title, "some value"
    = f.button :submit
  </code></pre>
  
  <p>results in this error:</p>
  
  <pre><code>undefined method `hidden' for #SimpleForm::FormBuilder:0x000001042b7cd0
  </code></pre>