Adding a delay to an observable pipe returns always null

[BenDevelopment]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ x] Bug report  
[ ] Performance issue
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question
[ ] Other... Please describe:

Current behavior

When a delay is added to an observable in a PipeTransform, the pipe returns always null.

Expected behavior

The pipe should returns the value returned by the observable.

Minimal reproduction of the problem with instructions

1. Create a pipe returning an observable of string with a delay.
   See exemple:

https://stackblitz.com/edit/angular-gitter-tut9xq?file=app%2Fapp.component.ts

What is the motivation / use case for changing the behavior?

The pipe should return the observable string value instead of null. The point is to avoid ExpressionChangedAfterItHasBeenCheckedError in a specific case with a delay(0) in the pipe.

Environment

Angular version: 6.0.2


Browser:
- [x] Chrome (desktop) version XX
- [ ] Chrome (Android) version XX
- [ ] Chrome (iOS) version XX
- [x] Firefox version XX
- [ ] Safari (desktop) version XX
- [ ] Safari (iOS) version XX
- [x] IE version XX
- [x] Edge version XX
 
For Tooling issues:
- Node version: XX  
- Platform:  

Others:

[trotyl]

Duplicate of #6696, #24133.

You are causing an infinite loop that never completes, scheduling new async task within template execution is not allowed.

[dawidgarus]

Change pipe to be pure and it will work

[BenDevelopment]

It works with a pure pipe thank you.

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