IndexError: list index out of range

[Felipe Reyes]

when tearing down a model the relation-departed hook fails with the stacktrace below. I think the interface should be checking if there are relations available before querying data from them at https://opendev.org/openstack/charm-interface-keystone/src/branch/master/requires.py#L48

unit-ironic-api-0: 14:32:12 ERROR unit.ironic-api/0.juju-log identity-service:10: Hook error:
Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-ironic-api-0/.venv/lib/python3.10/site-packages/charms/reactive/__init__.py", line 74, in main
    bus.dispatch(restricted=restricted_mode)
  File "/var/lib/juju/agents/unit-ironic-api-0/.venv/lib/python3.10/site-packages/charms/reactive/bus.py", line 390, in dispatch
    _invoke(other_handlers)
  File "/var/lib/juju/agents/unit-ironic-api-0/.venv/lib/python3.10/site-packages/charms/reactive/bus.py", line 359, in _invoke
    handler.invoke()
  File "/var/lib/juju/agents/unit-ironic-api-0/.venv/lib/python3.10/site-packages/charms/reactive/bus.py", line 181, in invoke
    self._action(*args)
  File "/var/lib/juju/agents/unit-ironic-api-0/charm/hooks/relations/keystone/requires.py", line 140, in departed
    self.update_flags()
  File "/var/lib/juju/agents/unit-ironic-api-0/charm/hooks/relations/keystone/requires.py", line 112, in update_flags
    if self.base_data_complete():
  File "/var/lib/juju/agents/unit-ironic-api-0/charm/hooks/relations/keystone/requires.py", line 147, in base_data_complete
    'service_host': self.service_host(),
  File "/var/lib/juju/agents/unit-ironic-api-0/charm/hooks/relations/keystone/requires.py", line 48, in _accessor_internal
    return self.relations[0].received_app_raw.get(
  File "/var/lib/juju/agents/unit-ironic-api-0/.venv/lib/python3.10/site-packages/charms/reactive/endpoints.py", line 654, in __getitem__
    return super().__getitem__(self._translate_key(key))
IndexError: list index out of range

[Felipe Reyes (freyes)]

probably the custom metaclass could be dropped in favor of the one provided by charms.reactive.