NestJS example does not work with root paths

The [starter example for Nest JS](https://github.com/vendia/serverless-express/tree/mainline/examples/basic-starter-nestjs) does not work with root paths.

## Steps to reproduce

```shell
git clone https://github.com/vendia/serverless-express.git
cd serverless-express/examples/basic-starter-nestjs
npm ci
```

Remove the path from the [demo controller's handler](https://github.com/vendia/serverless-express/blob/mainline/examples/basic-starter-nestjs/src/app.controller.ts#L8) so it [defaults to the root path for the controller](https://docs.nestjs.com/controllers#routing).

```shell
npm run sls:offline
```

Make a request to `http://localhost:3000/dev`.

The server responds with a `404` error of `Cannot GET null`.

---

I have confirmed that this does not occur when using Nest JS without Serverless:

```shell
nest new nest-test
cd nest-test
npm run start
```

Make a request to `http://localhost:3000`.

The server responds with the expected response.

examples/basic-starter-nestjs/src/app.controller.ts から始め、npm ci、npm run sls:offline、および http://localhost:3000/dev へのリクエストで問題を再現します。root controller のパスがどのように処理されるかを追跡し、リクエストが 404 Cannot GET null レスポンスを返さなくなったことを確認します。

索引モデルが issue の本文から書いたものです。