`NoneType: None` in juju debug-log

`NoneType: None` appears in juju logs after raising an exception. This log is useless and can be removed for clarity.

## Steps to reproduce
```
juju deploy postgresql --channel=16/stable
juju config postgresql plugin_address_standardizer_enable=true
juju debug-log -i postgresql
```

## Expected behavior
No `NoneType: None` line in log. Useless and not following proper log format

## Actual behavior
```
unit-postgresql-0: 13:12:05 ERROR unit.postgresql/0.juju-log __main__:cannot enable address_standardizer, extension required postgis to be enabled before
NoneType: None
unit-postgresql-0: 13:12:05 INFO juju.worker.uniter.operation ran "config-changed" hook (via hook dispatching script: dispatch)
```

## Versions

Operating system: 24.04
Juju CLI: 3.624
Juju agent: 3.6.24
Charm revision: 1158
LXD: 5.21/stable

Start by reproducing the issue with the listed juju deploy, juju config, and juju debug-log commands, then trace the config-changed hook handling for the postgresql charm. Done means the extension error remains useful and the separate `NoneType: None` line no longer appears in juju debug-log output.

Written by the indexing model from the issue text.