Pulls the class elements from child <a> element and puts them on the parent <li> item. Useful if you want classes you added with the menu_attributes module to be used on the parent <li>, since those classes are placed on the <a> element itself.

Drupal 7: Child CSS Class for Parent LI

function THEME_preprocess_menu_link(&$variables) {
  $element = &$variables['element'];
  
  if (!empty($element['#original_link']['options']['attributes']['class'])) {
    foreach($element['#original_link']['options']['attributes']['class'] as $class) {
      $element['#attributes']['class'][] = $class;
    }
  }
}