title: Rails simple_form gem is adding a green border to inputs that are pre-populated
body: <p>I am having a problem with the rails simple_form gem. I am using bootstrap 4 along with it.</p>
  
  <p>I have installed the gem by adding <code>gem 'simple_form'</code> to the Gemfile. I have also run the generator via <code>rails g simple_form:install --bootstrap</code>.</p>
  
  <p>Simple Form works almost perfectly in my app. Here is an example using a model called 'Store' that has one string attribute: 'name'.</p>
  
  <pre><code>&lt;%= simple_form_for @store do |f| %&gt;
    &lt;%= f.input :name %&gt;
    &lt;%= f.button :submit, class: "btn-primary" %&gt;
    &lt;%= link_to "Cancel", stores_url, class: %w[btn btn-danger] %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>The only problem I'm having with this code is that when the form is used for the update page, simple_form adds an '.is-valid' class to the input element which causes bootstrap to add a green border to the field. This does not happen when the field is not pre-filled such as when using the form for the 'new' action.</p>
  
  <p>Thanks</p>