title: Rails hidden field undefined method 'merge' error
body: <p>I wanna do something like this in rails
  </p>
  
  <p>Here is what I have so far in rails: </p>
  
  <pre><code>&lt;%= form_for @order do |f| %&gt;
    &lt;%= f.hidden_field :service, "test" %&gt;
    &lt;%= f.submit %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>But then I get this error:</p>
  
  <pre><code>undefined method `merge' for "test":String
  </code></pre>
  
  <p>How can I pass values in my hidden_field in rails?</p>