def default_url *args
      if (version = args.first) && version.respond_to?(:to_sym)
        raise ArgumentError, "Version #{version} doesn't exist!" if versions[version.to_sym].nil?
        # recursively proxy to version
        versions[version.to_sym].default_url(*args[1..-1])
      else
        ::ActionController::Base.helpers.asset_path(
          "loyal_core/fallbacks/#{impl_model_name_underscore}/#{mounted_as}/" + [version_name, "missing.gif"].compact.join('_')
        )
      end

      # For Rails 3.1+ asset pipeline compatibility:
      # "/images/fallbacks/#{impl_model_name_underscore}/#{mounted_as}/" + ["missing.gif", version_name].compact.join('_')
    
      # "/images/fallback/" + [version_name, "default.png"].compact.join('_')
    end
def default_url *args
      if (version = args.first) && version.respond_to?(:to_sym)
        raise ArgumentError, "Version #{version} doesn't exist!" if versions[version.to_sym].nil?
        # recursively proxy to version
        versions[version.to_sym].default_url(*args[1..-1])
      else
        ::ActionController::Base.helpers.asset_path(
          "loyal_core/fallbacks/#{impl_model_name_underscore}/#{mounted_as}/" + [version_name, "missing.gif"].compact.join('_')
        )
      end

      # For Rails 3.1+ asset pipeline compatibility:
      # "/images/fallbacks/#{impl_model_name_underscore}/#{mounted_as}/" + ["missing.gif", version_name].compact.join('_')
    
      # "/images/fallback/" + [version_name, "default.png"].compact.join('_')
    end
Provide a default URL as a default if there hasn't been a file uploaded:
 def default_url
   # For Rails 3.1+ asset pipeline compatibility:
   # asset_path("fallback/" + [version_name, "default.png"].compact.join('_'))

   "/images/fallback/" + [version_name, "default.png"].compact.join('_')
 end