Keep getting error: "invalid json response body at reason: Unexpected end of JSON input"

```
FetchError: invalid json response body at reason: Unexpected end of JSON input

at node_modules/node-fetch/lib/index.js:272:32
```

Here is my code:
```
const response = await request(app)
.get('/api/demos')
.expect(200);
```

Start by reproducing the request shown against the /api/demos endpoint and inspect the response body and headers. Read the node_modules/node-fetch/lib/index.js stack location and determine whether the failure is in the endpoint response or Supertest's handling; done means the cause and a concrete project change are identified.

Written by the indexing model from the issue text.