Please fill in this template.
- [X] Use a meaningful title for the pull request. Include the name of the package modified.
- [X] Test the change in your own code. (Compile and run.)
- [X] Add or edit tests to reflect the change. (Run with `npm test`.)
- [X] Follow the advice from the [readme](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/README.md#make-a-pull-request).
- [X] Avoid [common mistakes](https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/README.md#common-mistakes).
- [X] Run `npm run lint package-name` (or `tsc` if no `tslint.json` is present).
Select one of these and delete the others:
If changing an existing definition:
- [X] Provide a URL to documentation or source code which provides context for the suggested changes:
```
import * as fs from "fs";
fs.readdir("./non-existing-dir", (error, files) => {
// Will print "error: ..."
console.log("error: ", error);
// Will print "files: undefined"
console.log("files: ", files);
});
fs.readdir("./existing-dir", (error, files) => {
// Will print "error: null"
console.log("error: ", error);
// Will print "files: ..."
console.log("files: ", files);
});
```
- [X] Increase the version number in the header if appropriate.
- [x] If you are making substantial changes, consider adding a `tslint.json` containing `{ "extends": "dtslint/dt.json" }`.
