title: ng-select items not visible
body: <p>I added ng-select to a new Angular 11 application, and it seems to be working fine until I open the dropdown. When I open the dropdown, I can select items but I don't really see them. There's 3 errors in the console every time I open the dropdown:</p>
  <pre><code>zone-evergreen.js:659 Unhandled Promise rejection: Cannot read properties of undefined (reading 'clientHeight') ; Zone: &lt;root&gt; ; Task: Promise.then ; Value: TypeError: Cannot read properties of undefined (reading 'clientHeight')
      at ng-select.js:2268:1
      at ZoneDelegate.invoke (zone-evergreen.js:364:1)
      at Zone.run (zone-evergreen.js:123:1)
      at zone-evergreen.js:857:1
      at ZoneDelegate.invokeTask (zone-evergreen.js:399:1)
      at Zone.runTask (zone-evergreen.js:167:1)
      at drainMicroTaskQueue (zone-evergreen.js:569:1)
      at ZoneTask.invokeTask [as invoke] (zone-evergreen.js:484:1)
      at invokeTask (zone-evergreen.js:1621:1)
      at HTMLDivElement.globalZoneAwareCallback (zone-evergreen.js:1647:1) TypeError: Cannot read properties of undefined (reading 'clientHeight')
      at http://localhost:4200/vendor.js:12640:59
      at ZoneDelegate.invoke (http://localhost:4200/polyfills.js:9528:30)
      at Zone.run (http://localhost:4200/polyfills.js:9287:47)
      at http://localhost:4200/polyfills.js:10021:40
      at ZoneDelegate.invokeTask (http://localhost:4200/polyfills.js:9563:35)
      at Zone.runTask (http://localhost:4200/polyfills.js:9331:51)
      at drainMicroTaskQueue (http://localhost:4200/polyfills.js:9733:39)
      at ZoneTask.invokeTask [as invoke] (http://localhost:4200/polyfills.js:9648:25)
      at invokeTask (http://localhost:4200/polyfills.js:10785:18)
      at HTMLDivElement.globalZoneAwareCallback (http://localhost:4200/polyfills.js:10811:21)
  </code></pre>
  <pre><code>ERROR TypeError: Cannot read properties of undefined (reading 'nativeElement')
      at NgDropdownPanelComponent.ngOnInit (ng-select.js:2102:1)
      at callHook (core.js:4776:1)
      at callHooks (core.js:4746:1)
      at executeInitAndCheckHooks (core.js:4698:1)
      at selectIndexInternal (core.js:8140:1)
      at Module.ɵɵadvance (core.js:8123:1)
      at NgSelectComponent_ng_dropdown_panel_13_Template (ng-select.js:244:21)
      at executeTemplate (core.js:9269:1)
      at refreshView (core.js:9138:1)
      at refreshEmbeddedViews (core.js:10245:1)
  </code></pre>
  <pre><code>core.js:5973 ERROR TypeError: Cannot read properties of undefined (reading 'nativeElement')
      at NgDropdownPanelComponent.ngOnInit (ng-select.js:2102:1)
      at callHook (core.js:4776:1)
      at callHooks (core.js:4746:1)
      at executeInitAndCheckHooks (core.js:4698:1)
      at selectIndexInternal (core.js:8140:1)
      at Module.ɵɵadvance (core.js:8123:1)
      at NgSelectComponent_ng_dropdown_panel_13_Template (ng-select.js:244:21)
      at executeTemplate (core.js:9269:1)
      at refreshView (core.js:9138:1)
      at refreshEmbeddedViews (core.js:10245:1)
  </code></pre>
  <p>I am honestly not sure what to even look at. It seems to function properly, but it's displayed incorrectly.</p>
  <p>package.json (all Angular packages are at 11.0.1):</p>
  <pre><code>&quot;@ng-select/ng-select&quot;: &quot;^2.20.5&quot;,
  </code></pre>
  <p>This is the template:</p>
  <pre class="lang-html prettyprint-override"><code>&lt;ng-select [items]=&quot;types&quot;
    bindLabel=&quot;name&quot;
    bindValue=&quot;id&quot;
    placeholder=&quot;Select type&quot;
    [(ngModel)]=&quot;selectedType&quot;&gt;
  &lt;/ng-select&gt;
  </code></pre>
  <p>I have added <code>NgSelectModule</code> to my app.module.ts, too.</p>