fix rebase error

asyncua/client/client.py

@@ -29,6 +29,10 @@ class Client:
     use UaClient object, available as self.uaclient
     which offers the raw OPC-UA services interface.
     """
+
+    _username = None
+    _password = None
+
     def __init__(self, url: str, timeout: float = 4, watchdog_intervall: float = 1.0):
         """
         :param url: url of the server.