Produces undefined if `values` is empty or undefined

Nobody has claimed this yet.

If `values` is not specified result is always a bunch of `undefined`

```
new ReplacePlugin({
include: /serviceManager/,
patterns: [
{
regex: /var IS_WEB = [^;]+;/,
value: 'var IS_WEB = true;'
}
]
})
```
Calls on file content:
```
mod._source._value.replace(/(?:)/g, k => vals[k]);
```

Can be easily fixed:
```
if(keys.length) {
mod._source._value.replace(REGEXP, k => vals[k]);
}
```

Start from the ReplacePlugin implementation that builds the replacement regular expression and invokes replace on the file content. Reproduce the issue with the configuration shown and verify that an empty or undefined values collection leaves the original content unchanged rather than producing undefined output.

Written by the indexing model from the issue text.