How do I unit test an Angular HttpClient 204 response?

Our REST service returns 204's for a no data scenario. But I cannot figure out how to test for this scenario.

it('can handle no data', (done) => {
  const testData = service.getDummyData();
  service.dataChanged$.subscribe(
    (data: Data[]) => {
      expect(data).toBeUndefined();
      done();
    }
  );
  service.getData();
  const request: TestRequest = backend.expectOne(MyService.URL);
  request.flush(undefined, { status: 204, statusText: 'No Data' });
});

I've tried passing:

• undefined and false
  • Error: Automatic conversion to JSON is not supported for response type.
• null
  • response data is the string "null"

So, what should I be passing to the flush function to send an empty response? I test the response in the service (simplified):

this.http.get<Data[]>(MyService.URL)
  .first().subscribe(
    (data: Data[]) => {
      if (data) {
        this.dataChanged$.next(data);
      } else {
        Logger.error(MyService.name, 'getData', 'No data.');
        this.dataChanged$.next(undefined);
      }
    },
    (error: Error) => {
        Logger.error(MyService.name, 'getData', error.message);
      this.dataChanged$.next(undefined);
    }
  );

So, the simple answer is, pass '' to flush():

request.flush('', { status: 204, statusText: 'No Data' });