title: CarrierWave gem isn't uploading, so why is there no raised exception?
body: <p>I'm attempting to install CarrierWave gem on ActiveAdmin in rails, and the setup seemed easy enough. However, when I attempt to upload a test image to the <code>/public/uploads</code> directory, the image isn't saved. What's more irritating is the fact that there is no exception being raised, so I don't know where to look in order to find the issue. I can create a post, browse for an image, select that image, and submit the post in order to be saved, but I still end up with <code>IMAGE: EMPTY</code> on the show page in ActiveAdmin as shown below. In the image, I wrote a lorem ipsum post that included an image, and I saved it. </p>
  
  <p><strong>How to I actually get the uploader to upload?</strong></p>
  
  <hr>
  
  <p><em>ruby 1.9.3p547 (2014-05-14 revision 45962) [x86_64-darwin10.8.0]</em></p>
  
  <p><em>Rails 4.1.6</em></p>
  
  <hr>
  
  <p><em>This is the show page for a single Post object within ActiveAdmin</em></p>
  
  <p><img src="https://i.stack.imgur.com/8y5Yt.png" alt="Image not uploading"></p>
  
  <hr>
  
  <p><em>This is a full page screenshot of the form in question</em></p>
  
  <p><img src="https://i.stack.imgur.com/ntWxl.png" alt="full page"></p>
  
  <p><em>The same form, but zoomed in. Obviously, I wasn't trying to upload an image in this screenshot.</em></p>
  
  <p><img src="https://i.stack.imgur.com/m4vu8.png" alt="zoomed in on form"></p>
  
  <hr>
  
  <p><em>/app/uploaders/image_uploader.rb</em></p>
  
  <pre><code>class ImageUploader &lt; CarrierWave::Uploader::Base
  
      storage :file
  
      def store_dir
          "public/uploads"
      end
  
  end
  </code></pre>
  
  <p><em>/app/models/post.rb</em></p>
  
  <pre><code>class Post &lt; ActiveRecord::Base
  
      belongs_to :category
  
      scope :rails, -&gt; { where(category_id: 1) }
  
      extend FriendlyId
      friendly_id :title, use: [:slugged, :finders]
  
      mount_uploader :image, ImageUploader
  
  end
  </code></pre>