Bluetooth on Ubuntu Core: Dbus signature error


I am developing a snap with the Bluetooth as a peripheral, using Python.
For that I choosed the dbus API from Bluez to quick start.
The problem is that the snap worked perfectly in the Ubuntu 16.04 but in Ubuntu Core I’ve got the error:

ERROR:dbus.connection:Unable to set arguments (dbus.ObjectPath('/org/bluez/example/service1'), {}) according to signature None: <type 'exceptions.ValueError'>: Unable to guess signature from an empty dict
Traceback (most recent call last):
  File "/snap/wg/x1/lib/python2.7/site-packages/dbus/", line 604, in msg_reply_handler
  File "/snap/wg/x1/lib/python2.7/site-packages/dbus/", line 401, in _introspect_reply_handler
  File "/snap/wg/x1/lib/python2.7/site-packages/dbus/", line 387, in _introspect_execute_queue
    proxy_method(*args, **keywords)
  File "/snap/wg/x1/lib/python2.7/site-packages/dbus/", line 137, in __call__
  File "/snap/wg/x1/lib/python2.7/site-packages/dbus/", line 584, in call_async
    message.append(signature=signature, *args)
ValueError: Unable to guess signature from an empty dict

What is going wrong? The version of bluez in the Ubuntu Core is 5.47-3