Warning: ksort() expects parameter 1 to be array, null given in ksort()

Whenever i save a node im getting this error.

Warning: ksort() expects parameter 1 to be array, null given in ksort() (line 3114 of .../includes/common.inc). =>

Using krumo backtrace it suggests the error comes from this module.
Particularly where it adds inline CSS for fonts loaded via AJAX.

Fonts are working but im still getting this error. Any ideas why?

here is the backtrace:

... (Array, 11 elements)
10: ksort() (Array, 1 element)
 9: drupal_group_css() (Array, 2 elements)
 8: drupal_pre_render_styles() (Array, 2 elements)
 7: drupal_render() (Array, 2 elements)
 6: fonts_com_ajax_render_alter() (Array, 2 elements)
 5: drupal_alter() (Array, 2 elements)
 4: ajax_render() (Array, 2 elements)
 3: ajax_deliver() (Array, 2 elements)
 2: drupal_deliver_page() (Array, 2 elements)
 1: menu_execute_active_handler() (Array, 2 elements)
 0: main() (Array, 2 elements)