title: paperclip where to place the missing.png default image?
body: <p>I use paperclip in my app, but my controller tests are failing because of: </p>
  
  <pre><code>BlogsControllerTest#test_should_update_blog:
  Paperclip::AdapterRegistry::NoHandlerError: No handler found for "/images/original/missing.png"
      /Users/user/.rvm/gems/ruby-2.1.2/gems/paperclip-3.5.2/lib/paperclip/io_adapters/registry.rb:19:in `handler_for'
      /Users/user/.rvm/gems/ruby-2.1.2/gems/paperclip-3.5.2/lib/paperclip/io_adapters/registry.rb:29:in `for'
      /Users/user/.rvm/gems/ruby-2.1.2/gems/paperclip-3.5.2/lib/paperclip/attachment.rb:96:in `assign'
  </code></pre>
  
  <p>I'm not sure where I should place the <code>missing.png</code> image in my code, I tried in <code>public/assets/original/missing.png</code> but it doesn't seem to manage it.</p>
  
  <p>Also there's something odd: I have a <code>paperclip.rb</code> initializer line: </p>
  
  <pre><code>Paperclip::Attachment.default_options[:default_url] = "/images/default_image.png"
  </code></pre>
  
  <p>but still the app is looking for the <code>missing.png</code></p>
  
  <p>UPDATE: ok I figured that the default_url was overridden in the model:</p>
  
  <pre><code>has_attached_file :image, styles: { big: "1200X630&gt;", thumb: "150X150" }, default_url: "/images/:style/missing.png"
  </code></pre>
  
  <p>I still don't know where to place the image. </p>
  
  <p>UPDATE2: </p>
  
  <p>the entire paperclip initializer: </p>
  
  <pre><code>Paperclip::Attachment.default_options[:styles] = { thumb: "100x100#",  small: "200x200#",  screen: "800x600#"}
  Paperclip::Attachment.default_options[:default_url] = "/images/missing.png"
  Paperclip::Attachment.default_options[:path] = ":rails_root/public/assets/:class/:attachment/:id_partition/:style/:hash.:extension"
  Paperclip::Attachment.default_options[:url] = "/assets/:class/:attachment/:id_partition/:style/:hash.:extension"
  Paperclip::Attachment.default_options[:hash_secret] = "XXXXXXXXXXXXXXXXX"
  Paperclip.registered_attachments_styles_path = "public/assets/paperclip_attachments2.yml"
  </code></pre>
  
  <p>UPDATE3: checking the paperclip code that actually rises the code, the exception is risen by <a href="https://github.com/thoughtbot/paperclip/blob/v3.5.2/lib/paperclip/io_adapters/registry.rb#L16-L19" rel="noreferrer">this piece of code</a>, which is basically testing all the adapters available, the one that looks like the closest to what I want to do is the <a href="https://github.com/thoughtbot/paperclip/blob/v3.5.2/lib/paperclip/io_adapters/file_adapter.rb#L21" rel="noreferrer"><code>fileAdapter</code></a> which tests if the string passed is a File. </p>
  
  <p>I'm quite surprised from finding this, I thing I might be getting something wrong here. If I exchange the initializer line to: </p>
  
  <pre><code>Paperclip::Attachment.default_options[:default_url] = File.new "public/images/missing.png"
  </code></pre>
  
  <p>then the exception is different: </p>
  
  <pre><code>BlogsControllerTest#test_should_update_blog:
  NoMethodError: undefined method `gsub' for #&lt;File:public/images/missing.png&gt;
      /Users/user/.rvm/gems/ruby-2.1.2/gems/paperclip-3.5.2/lib/paperclip/interpolations.rb:33:in `block in interpolate'
      /Users/user/.rvm/gems/ruby-2.1.2/gems/paperclip-3.5.2/lib/paperclip/interpolations.rb:32:in `each'
  </code></pre>
  
  <p>UPDATE4: this is what the test looks like: </p>
  
  <pre><code>  test "should update blog" do
      put :update, id: @blog, blog: { 
        author_id: @blog.author_id, 
        body: @blog.body, 
        image: @blog.image, 
        title: @blog.title
      }
      assert_redirected_to blog_path(assigns(:blog))
    end
  
   test "should create blog" do
      assert_difference('Blog.count') do
        post :create, blog: { 
          author_id: @blog.author_id, 
          body: @blog.body, 
          image: @blog.image, 
          title: @blog.title }
      end
  
      assert_redirected_to blog_path(assigns(:blog))
    end
  </code></pre>
  
  <p>then: </p>
  
  <pre><code>@blog.image.class
  =&gt; Paperclip::Attachment
  @blog.image.url
  =&gt; "/images/missing.png"
  </code></pre>