$ gnome-tweak-tool
WARNING : Shell not installed or running
WARNING : Error detecting shell
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/gtweak/tweaks/tweak_group_shell_extensions.py", line 278, in __init__
    raise Exception("Shell not running or DBus service not available")
Exception: Shell not running or DBus service not available
INFO    : GSetting missing org.gnome.nautilus.desktop
INFO    : GSetting missing org.gnome.nautilus.desktop
INFO    : GSetting missing org.gnome.nautilus.desktop
INFO    : GSetting missing org.gnome.nautilus.desktop
INFO    : GSetting missing org.gnome.nautilus.desktop
WARNING : Shell not running
None
INFO    : GSetting missing org.gnome.mutter
INFO    : GSetting missing org.gnome.mutter
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/gtweak/app.py", line 39, in do_activate
    self.win = Window(self, model)
  File "/usr/lib/python2.7/site-packages/gtweak/tweakview.py", line 54, in __init__
    self._model.load_tweaks(self)
  File "/usr/lib/python2.7/site-packages/gtweak/tweakmodel.py", line 125, in load_tweaks
    mods = __import__("gtweak.tweaks", globals(), locals(), tweak_files, 0)
  File "/usr/lib/python2.7/site-packages/gtweak/tweaks/tweak_group_shell.py", line 65, in <module>
    sw = StaticWorkspaceTweak(size_group=sg, loaded=_shell_loaded)
  File "/usr/lib/python2.7/site-packages/gtweak/tweaks/tweak_group_shell.py", line 49, in __init__
    default = self.STATUS.keys()[self.STATUS.values().index(self.settings[self.key_name])]
ValueError: None is not in list