title: rails 4 paperclip: missing required attr_accessor
body: <p>I have a problem with paperclip and rails 4.
  When uploading an image, I get the following error:</p>
  
  <pre><code>Image model missing required attr_accessor for 'pic_file_name'
  </code></pre>
  
  <p>When adding the recommended attr_accessors</p>
  
  <pre><code>  attr_accessor :pic_file_name
    attr_accessor :pic_content_type
    attr_accessor :pic_file_size
    attr_accessor :pic_updated_at
  </code></pre>
  
  <p>the record is saved but the :pic column is empty, nothing was uploaded.</p>
  
  <p>I also tried whitelisting :pic_file_name</p>
  
  <pre><code> private
      # Use callbacks to share common setup or constraints between actions.
      def set_image
        @image = Image.find(params[:id])
      end
  
      # Never trust parameters from the scary internet, only allow the white list through.
      def image_params
        params.require(:image).permit(:title, :pic, :pic_file_name)
      end
  </code></pre>
  
  <p>but no success.</p>
  
  <p>Any ideas what is wrong here?</p>