Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.7/dbus/connection.py", line 589, in msg_reply_handler
    *message.get_args_list()))
  File "/usr/lib/pymodules/python2.7/dbus/proxies.py", line 406, in _introspect_error_handler
    self._introspect_execute_queue()
  File "/usr/lib/pymodules/python2.7/dbus/proxies.py", line 378, in _introspect_execute_queue
    proxy_method(*args, **keywords)
  File "/usr/lib/pymodules/python2.7/dbus/proxies.py", line 132, in __call__
    **keywords)
  File "/usr/lib/pymodules/python2.7/dbus/connection.py", line 566, in call_async
    message.append(signature=signature, *args)
ValueError: Unable to guess signature from an empty dict