title: First argument in form cannot contain nil or be empty - Rails 4
body: <p>I receive this error with my contact form in rails:</p>
  
  <pre><code>First argument in form cannot contain nil or be empty
  </code></pre>
  
  <p><strong>View:</strong>   </p>
  
  <pre><code>     &lt;%= form_for @contact do |f| %&gt;
       and so on.......
  </code></pre>
  
  <p><strong>Controller</strong></p>
  
  <pre><code>def new
      @contact = Contact.new
  end
   and so on....
  </code></pre>
  
  <p>I found related errors, but none of the solutions seems to fit my particular issue. Any clues to what could be causing this?</p>