Oh, I'm guessing it occurs when ```values``` is assigned the default value, or ```None```. So this can be prevented:

```
    def get(self, name, default=None):
        values = dict.get(self, name, None)
        if not values:
            return default
        setting = QObject.config.setting
        if setting["write_id3v23"]:
            return setting["id3v23_join_with"].join(values)
        else:
            return MULTI_VALUED_JOINER.join(values)
```