properly structuring the menu_link array

I've installed the zen theme framework and noticed the following errors (abridged for brevity):

Notice: Undefined index: class in zen_preprocess_menu_link() (line 621 of /path/to/drupal/sites/all/themes/zen/template.php).
Warning: Invalid argument supplied for foreach() in zen_preprocess_menu_link() (line 621 of /path/to/drupal/sites/all/themes/zen/template.php).
Warning: array_unshift() expects parameter 1 to be array, null given in zen_preprocess_menu_link() (line 637 of /path/to/drupal/sites/all/themes/zen/template.php).

Some digging around, here are some clues:

https://drupal.org/node/1841016

It seems that Zen (and apparently Adaptive Themes) requires $variables['element']['#localized_options']['attributes']['class'] to be specified in the menu_link array.

I've taken a look here: https://api.drupal.org/api/drupal/includes%21menu.inc/function/theme_men..., however the structure is different from you code.

I'm actually having no luck figuring this one out - any help would be greatly appreciated.