Comment 8 for bug 2042405

It seems juju would fail if the value is empty.

2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: 2024-01-06 05:47:06 WARNING unit.ceph-mon/0.config-changed logger.go:60 Error EINVAL: unrecognized config option 'mgr/prometheus/rbd_stats_pools'
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: 2024-01-06 05:47:06 ERROR unit.ceph-mon/0.juju-log server.go:316 Uncaught exception while in charm code:
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: Traceback (most recent call last):
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: File "./src/charm.py", line 310, in <module>
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: main(CephMonCharm)
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: File "/var/lib/juju/agents/unit-ceph-mon-0/charm/venv/ops/main.py", line 436, in main
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: _emit_charm_event(charm, dispatcher.event_name)
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: File "/var/lib/juju/agents/unit-ceph-mon-0/charm/venv/ops/main.py", line 144, in _emit_charm_event
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: event_to_emit.emit(*args, **kwargs)
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: File "/var/lib/juju/agents/unit-ceph-mon-0/charm/venv/ops/framework.py", line 351, in emit
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: framework._emit(event)
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: File "/var/lib/juju/agents/unit-ceph-mon-0/charm/venv/ops/framework.py", line 853, in _emit
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: self._reemit(event_path)
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: File "/var/lib/juju/agents/unit-ceph-mon-0/charm/venv/ops/framework.py", line 942, in _reemit
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: custom_handler(event)
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: File "/var/lib/juju/agents/unit-ceph-mon-0/charm/venv/ops_openstack/core.py", line 260, in _on_config
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: self.on_config(event)
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: File "./src/charm.py", line 87, in on_config
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: if hooks.config_changed():
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: File "/var/lib/juju/agents/unit-ceph-mon-0/charm/venv/charmhelpers/contrib/hardening/harden.py", line 90, in _harden_inner2
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: return f(*args, **kwargs)
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: File "/var/lib/juju/agents/unit-ceph-mon-0/charm/src/ceph_hooks.py", line 381, in config_changed
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: mgr_config_set_rbd_stats_pools()
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: File "/var/lib/juju/agents/unit-ceph-mon-0/charm/src/utils.py", line 427, in mgr_config_set_rbd_stats_pools
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: ceph_utils.mgr_config_set(
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: File "/var/lib/juju/agents/unit-ceph-mon-0/charm/venv/charms_ceph/utils.py", line 3569, in ceph_config_set
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: subprocess.check_call(['ceph', 'config', 'set', who, name, value])
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: File "/usr/lib/python3.8/subprocess.py", line 364, in check_call
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: raise CalledProcessError(retcode, cmd)
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: subprocess.CalledProcessError: Command '['ceph', 'config', 'set', 'mgr', 'mgr/prometheus/rbd_stats_pools', '']' returned non-zero exit status 22.
2024-01-06 05:47:08 [ERROR] unit-ceph-mon-0.log: 2024-01-06 05:47:07 ERROR juju.worker.uniter.operation runhook.go:153 hook "config-changed" (via hook dispatching script: dispatch) failed: exit status 1