Nebular: Tree Grid does not work

[bagerman]

Issue type

I'm submitting a ... (check one with "x")

• [x] bug report
• [] feature request

Issue description

Current behavior:

The following exception is thrown while trying to integrate TreeGrid component by following example provided in documentation for the Data Source use
This is html code at line referenced below in stack : at AllAnalyticsComponent_Template (all-analytics.component.html:5)
<table [nbTreeGrid]="source">
Exception stack
```ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'nativeElement' of null
TypeError: Cannot read property 'nativeElement' of null
at new CdkTable (table.js:1265)
at new NbTable (index.js:18425)
at new NbTreeGridComponent (index.js:25275)
at NodeInjectorFactory.NbTreeGridComponent_Factory [as factory] (index.js:25416)
at getNodeInjectable (core.js:4029)
at instantiateAllDirectives (core.js:7963)
at createDirectivesInstances (core.js:7329)
at Module.ɵɵelementStart (core.js:13901)
at AllAnalyticsComponent_Template (all-analytics.component.html:5)
at executeTemplate (core.js:7302)
at resolvePromise (zone-evergreen.js:798)
at resolvePromise (zone-evergreen.js:750)
at zone-evergreen.js:860
at ZoneDelegate.invokeTask (zone-evergreen.js:399)
at Object.onInvokeTask (core.js:27424)
at ZoneDelegate.invokeTask (zone-evergreen.js:398)
at Zone.runTask (zone-evergreen.js:167)
at drainMicroTaskQueue (zone-evergreen.js:569)
at ZoneTask.invokeTask [as invoke] (zone-evergreen.js:484)
at invokeTask (zone-evergreen.js:1621)

**Expected behavior:**
<!-- Describe what the behavior would be without the bug. -->
I would expect the TreeGrid to show up with no errors

**Steps to reproduce:**
<!--  Please explain the steps required to duplicate the issue, especially if you are able to provide a sample application. -->
Copy provided example and try to run

**Related code:**
<!-- 
If you are able to illustrate the bug or feature request with an example, please provide a sample application via one of the following means:

A sample application via GitHub

StackBlitz [StackBlitz Seed Project](https://stackblitz.com/github/akveo/nebular-seed)


-->

see documentation code

### Other information:
I am using Nebular v6 and Angular v1
**npm, node, OS, Browser**

**Angular, Nebular**

"@akveo/ng2-completer": "^9.0.1",
"@angular/animations": "^10.0.11",
"@angular/cdk": "^10.1.3",
"@angular/common": "^10.0.11",
"@angular/compiler": "^10.0.11",
"@angular/core": "^10.0.11",
"@angular/forms": "^10.0.11",
"@angular/google-maps": "^9.1.0",
"@angular/platform-browser": "^10.0.11",
"@angular/platform-browser-dynamic": "^10.0.11",
"@angular/router": "^10.0.11",
"@asymmetrik/ngx-leaflet": "3.0.1",
"@nebular/auth": "6.0.0",
"@nebular/eva-icons": "6.0.0",
"@nebular/security": "6.0.0",
"@nebular/theme": "6.0.0",

```

[sefasaid]

same here

[vsct-jburet]

same issue

[rrruuuyyy]

same issue

[sayax]

same issue

[yggg]

There is a breaking change in the Angular CDK introduced in the patch update 10.1.2 (see issue in cdk repo for details). To fix the error downgrade to @angular/[email protected]. Once fix released you can upgrade to the latest version of cdk.
Closing as unrelated to Nebular.