Traceback (most recent call last):
  File "/usr/share/software-center/softwarecenter/ui/gtk3/panes/softwarepane.py", line 416, in on_query_complete
    self._is_in_search_mode())
  File "/usr/share/software-center/softwarecenter/ui/gtk3/views/appview.py", line 203, in display_matches
    self._use_combobox_with_sort_by_search_ranking()
  File "/usr/share/software-center/softwarecenter/ui/gtk3/views/appview.py", line 157, in _use_combobox_with_sort_by_search_ranking
    if self._get_combo_children() == 4:
  File "/usr/share/software-center/softwarecenter/ui/gtk3/views/appview.py", line 154, in _get_combo_children
    return len(self.sort_methods_combobox.get_model())
TypeError: object of type 'NoneType' has no len()