title: Rails 5 Simple Form does not display errors
body: <p>The only way I can get my Simple form to display an error is via </p>
  
  <pre><code>  &lt;% errors = f.object.errors.messages.collect { |k,v| "#{k}: #{v}" if v.length &gt; 0 }.join("\n")%&gt;
    &lt;%= f.error_notification message: "Errors: #{errors}" %&gt;
  </code></pre>
  
  <p>Which seems way too complicated.</p>
  
  <p><strong>Scenario:</strong></p>
  
  <p>User table and nested, polymorphic table of social_profile links (facebook, twitter, etc).</p>
  
  <p>If the user does not fill out any of the nested form when creating a new account, the profile inputs/params are empty strings and it saves fine. </p>
  
  <p>However, if the user deletes all the profile links' input fields then the association to the social_profile table will not be created. Thus, if the user later tries to edit his account the nested social_profile form will not be displayed. </p>
  
  <p>Adding <code>validates :social_profile, presence: true, associated: true</code> to the User's model prevents this error from happening, but there is no indication of what occurred given to the user. The best I could come up with is the original code, but it seems like there should be a better way.</p>