Unable to dump policy using oslopolicy-policy-generator for glance

Steps to reproduce:

$ cd glance/ # Using the master branch
$ python3 -m venv vvv
(vvv) $ source vvv/bin/activate
(vvv) $ pip install oslo.policy
(vvv) $ pip install -r requirements.txt
(vvv) $ python setup.py install
(vvv) $ oslopolicy-policy-generator --namespace glance
WARNING:stevedore.named:Could not load glance
Traceback (most recent call last):
  File "/home/cyril/tmp/oslopo/glance/vvv/bin/oslopolicy-policy-generator", line 10, in <module>
    sys.exit(generate_policy())
  File "/home/cyril/tmp/oslopo/glance/vvv/lib/python3.7/site-packages/oslo_policy/generator.py", line 338, in generate_policy
    _generate_policy(conf.namespace, conf.output_file)
  File "/home/cyril/tmp/oslopo/glance/vvv/lib/python3.7/site-packages/oslo_policy/generator.py", line 283, in _generate_policy
    enforcer = _get_enforcer(namespace)
  File "/home/cyril/tmp/oslopo/glance/vvv/lib/python3.7/site-packages/oslo_policy/generator.py", line 87, in _get_enforcer
    enforcer = mgr[namespace].obj
  File "/home/cyril/tmp/oslopo/glance/vvv/lib/python3.7/site-packages/stevedore/extension.py", line 326, in __getitem__
    return self._extensions_by_name[name]
KeyError: 'glance'