IPU blows up on relation broken (ops 2.10)

[PietroPasotti]

Bug Description

on destroying an ingress-per-unit-relation, the charm errors out because self.relation is None in IPU lib wrapper.

To Reproduce

juju deploy cos-lite --trust
juju remove-application traefik

Environment

                juju info v0.1                    
──────────────┬────────────────────────────────┐  
 jhack        │ 0.3.32                         │  
 python       │ 3.10.12 (/bin/python3)         │  
 juju-* snaps │                                │  
juju agent version   |  3.1.6   |
 microk8s     │ MicroK8s v1.29.2 revision 6591 │  
 lxd          │ 5.20                           │  
 multipass    │ 1.13.1                         │  
 multipassd   │ 1.13.1                         │  
 os           │ Ubuntu 22.04.4 LTS             │  
 kernel       │ Linux 6.5.0-21-generic x86_64  │  
──────────────┴────────────────────────────────┘  

Relevant log output

unit-prometheus-0: 13:31:02 ERROR unit.prometheus/0.juju-log ingress:7: Uncaught exception while in charm code:                              
Traceback (most recent call last):                                                                                                           
  File "./src/charm.py", line 1074, in <module>                                                                                              
    main(PrometheusCharm)                                                                                                                    
  File "/var/lib/juju/agents/unit-prometheus-0/charm/venv/ops/main.py", line 456, in main                                                    
    _emit_charm_event(charm, dispatcher.event_name)                                                                                          
  File "/var/lib/juju/agents/unit-prometheus-0/charm/venv/ops/main.py", line 144, in _emit_charm_event                                       
    event_to_emit.emit(*args, **kwargs)                                                                                                      
  File "/var/lib/juju/agents/unit-prometheus-0/charm/venv/ops/framework.py", line 352, in emit                                               
    framework._emit(event)                                                                                                                   
  File "/var/lib/juju/agents/unit-prometheus-0/charm/venv/ops/framework.py", line 865, in _emit                                              
    self._reemit(event_path)                                                                                                                 
  File "/var/lib/juju/agents/unit-prometheus-0/charm/venv/ops/framework.py", line 955, in _reemit                                            
    custom_handler(event)                                                                                                                    
  File "/var/lib/juju/agents/unit-prometheus-0/charm/lib/charms/traefik_k8s/v1/ingress_per_unit.py", line 753, in _handle_relation           
    self.on.revoked_for_unit.emit(self.relation)  # type: ignore                                                                             
  File "/var/lib/juju/agents/unit-prometheus-0/charm/venv/ops/framework.py", line 352, in emit                                               
    framework._emit(event)                                                                                                                   
  File "/var/lib/juju/agents/unit-prometheus-0/charm/venv/ops/framework.py", line 860, in _emit                                              
    self.save_snapshot(event)                                                                                                                
  File "/var/lib/juju/agents/unit-prometheus-0/charm/venv/ops/framework.py", line 729, in save_snapshot                                      
    data = value.snapshot()                                                                                                                  
  File "/var/lib/juju/agents/unit-prometheus-0/charm/venv/ops/charm.py", line 471, in snapshot                                               
    'relation_name': self.relation.name,                                                                                                     
AttributeError: 'NoneType' object has no attribute 'name'

Additional context

No response