withNaming - default modifier's delimiter is undefined

## Example

If I call it like this:

```js
const cn = withNaming({e: '__'});
```

```js
cn('bl')('el', { mod: 'val' });
// -> bl__elundefinedmodundefinedval
```

It only works if I explicitly specify the modifier

```js
withNaming({e: '__', m: '_'});
```