Notice: Undefined index: group in drupal_sort_css_js() ( ...

I am having this kind of notices in some of my sites that I use seventeen as admin theme:

Notice: Undefined index: group in drupal_sort_css_js() (line 3187  /home/.../includes/common.inc).
Notice: Undefined index: group in drupal_sort_css_js() (line 3187  /home/.../includes/common.inc).
Notice: Undefined index: group in drupal_sort_css_js() (line 3190  /home/.../includes/common.inc).
Notice: Undefined index: group in drupal_sort_css_js() (line 3187  /home/.../includes/common.inc).
Warning: uasort(): Array was modified by the user comparison function in drupal_get_css() (line 3121  /home/.../includes/common.inc).line
Notice: Undefined index: type in drupal_get_css() (line 3138  /home/.../includes/common.inc).line
Warning: ksort() expects parameter 1 to be array, null given in drupal_group_css() (line 3264  /home/.../includes/common.inc).
Notice: Undefined index: type in drupal_group_css() (line 3276  /home/.../includes/common.inc).
Notice: Undefined variable: group_keys in drupal_group_css() (line 3296  /home/.../includes/common.inc).
Notice: Undefined index: type in drupal_aggregate_css() (line 3337  /home/.../includes/common.inc).
Notice: Undefined index: type in drupal_pre_render_styles() (line 3457  /home/.../includes/common.inc).

I fixed it by adding the bellow at line 25 in template.php (function seventeen_css_alter()) :

if (isset($css['themes/seven/ie.css']['data']))

I dont know if this is the correct approach. Thanks