Traceback (most recent call last):
  File "/usr/share/software-center/softwarecenter/ui/gtk3/panes/availablepane.py", line 452, in on_db_reopen
    self.refresh_apps()
  File "/usr/share/software-center/softwarecenter/ui/gtk3/panes/availablepane.py", line 658, in refresh_apps
    SoftwarePane.refresh_apps(self, query)
  File "/usr/share/software-center/softwarecenter/ui/gtk3/panes/softwarepane.py", line 646, in refresh_apps
    self.app_view.clear_model()
  File "/usr/share/software-center/softwarecenter/ui/gtk3/views/appview.py", line 193, in clear_model
    return self.tree_view.clear_model()
  File "/usr/share/software-center/softwarecenter/ui/gtk3/widgets/apptreeview.py", line 121, in clear_model
    self.appmodel.clear()
AttributeError: 'NoneType' object has no attribute 'clear'