Handle juju/juju#20794

Signed-off-by: Marcelo Henrique Neppel <marcelo.neppel@canonical.com>

Author: marceloneppel

src/charm.py

@@ -439,6 +439,14 @@ def get_hostname_by_unit(self, _) -> str:
         return self._unit_ip
 
     def _on_secret_remove(self, event: SecretRemoveEvent) -> None:
+        # A secret removal (entire removal, not just a revision removal) causes
+        # https://github.com/juju/juju/issues/20794. This check is to avoid the
+        # errors that would happen if we tried to remove the revision in that case
+        # (in the revision removal, the label is present).
+        if event.secret.label is None:
+            logger.debug("Secret with no label cannot be removed")
+            return
+        logger.debug(f"Removing secret with label {event.secret.label} revision {event.revision}")
         event.remove_revision()
 
     def _on_get_primary(self, event: ActionEvent) -> None: