Questions about sourcemap

 Why is the upstream sourcemap not processed in the loader?
 > https://github.com/TypeStrong/ts-loader/blob/main/src/index.ts#L34

```js
function loader(this: webpack.LoaderContext<LoaderOptions>, contents: string, map?: Sourcemap) {
    if (map) {
       ...
    }
}
```