Cannot read property 'appendChild' of undefined when using Nebular Autocomplete

### Autocomplete module not allowing to edit

**I'm submitting a ...**

* [x] bug report
* [ ] feature request

### Issue description

**Current behavior:**
After setting up the autocomplete tag, when I try to type into the box, I get the error below.
core.js:5980 ERROR TypeError: Cannot read property 'appendChild' of undefined
at NbOverlayContainerAdapter._createContainer (index.js:2403)
at NbOverlayContainerAdapter.getContainerElement (overlay.js:725)
at NbOverlay._createHostElement (overlay.js:2591)
at NbOverlay.create (overlay.js:2558)
at NbOverlayService.create (index.js:2999)
at NbAutocompleteDirective.createOverlay (index.js:25129)
at NbAutocompleteDirective.initOverlay (index.js:25137)
at NbAutocompleteDirective.attachToOverlay (index.js:25123)
at NbAutocompleteDirective.show (index.js:24988)
at SafeSubscriber._next (index.js:25063)

**Expected behavior:**
I should see my options listed.

**Steps to reproduce:**
See same code in stackblitz below, does not work either.
https://stackblitz.com/edit/angular-tfa7r2?file=src/app/app.module.ts