code: @Override
      public String generateCssFileName(final DynamicSkinInstanceData data) {
          final PortletPreferences preferences = data.getPortletRequest().getPreferences();
          return getCssFileName(preferences);
      }
docs: Returns preference value as the CSS filename. If preference value is not found or if the
  value is empty, then a {@link DynamicSkinException} will be thrown.
  
  @see DynamicSkinCssFileNamer#generateCssFileName(DynamicSkinInstanceData)