tripleo-ansible-inventory is failing with a heatclient.exc.HTTPNotFound: ERROR: The Stack (overcloud) could not be found

When using tripleo-ansible-inventory script to generate a static inventory, it always fails:

(undercloud) [stack@undercloud ~]$ tripleo-ansible-inventory --static-inventory /home/stack/validations_static_inventory
Traceback (most recent call last):
  File "/usr/bin/tripleo-ansible-inventory", line 133, in <module>
    main()
  File "/usr/bin/tripleo-ansible-inventory", line 114, in main
    hclient)
  File "/usr/lib/python2.7/site-packages/tripleo_validations/inventory.py", line 61, in __init__
    self.stack_outputs = StackOutputs(self.configs.plan, self.hclient)
  File "/usr/lib/python2.7/site-packages/tripleo_validations/inventory.py", line 35, in __init__
    self.hclient.stacks.output_list(plan)['outputs']]
  File "/usr/lib/python2.7/site-packages/heatclient/v1/stacks.py", line 257, in output_list
    stack_identifier = self._resolve_stack_id(stack_id)
  File "/usr/lib/python2.7/site-packages/heatclient/v1/stacks.py", line 112, in _resolve_stack_id
    resp = self.client.get('/stacks/%s' % stack_id, redirect=False)
  File "/usr/lib/python2.7/site-packages/keystoneauth1/adapter.py", line 223, in get
    return self.request(url, 'GET', **kwargs)
  File "/usr/lib/python2.7/site-packages/heatclient/common/http.py", line 317, in request
    raise exc.from_response(resp)
heatclient.exc.HTTPNotFound: ERROR: The Stack (overcloud) could not be found.

Note that this behaviour is only happening from tripleo-validations master branch.
Moreover, running validations through the mistral framework is failing as well.