AttributeError: 'NoneType' object has no attribute 'rstrip'

If the optional keyword argument 'auth_url' is not supplied and 'auth_system' is not "keystone" (the optional keyword's default value) when instantiating the nova client then a traceback will be produced due to novaclient.client.HTTPClient.__init__ attempting to call the rstrip method on auth_url which obviously does not exist when auth_url is of the type None.

Traceback (most recent call last):
<snip>
  File "tests.py", line 113, in get_nova_client
    return novaclient.client.Client(version, username, password, tenant)
  File "/.../novaclient/client.py", line 473, in Client
    return client_class(*args, **kwargs)
  File "/.../novaclient/v1_1/client.py", line 111, in __init__
    http_log_debug=http_log_debug)
  File "/.../novaclient/client.py", line 98, in __init__
    self.auth_url = auth_url.rstrip('/')
AttributeError: 'NoneType' object has no attribute 'rstrip'