cdkStepper error

Bug, feature request, or proposal:

Bug

What is the current behavior?

Error message when using cdkStepper.

ERROR TypeError: Cannot read property '0' of undefined
at FocusKeyManager.push../node_modules/@angular/cdk/esm5/a11y.es5.js.ListKeyManager.updateActiveItem

What are the steps to reproduce?

<div cdkStepper>
 <cdk-step label="Step 1" [stepControl]="someformGroup">
 <button cdkStepperPrevious mat-button color="primary">Previous</button>
 <button cdkStepperNext mat-button color="primary">Next</button>
 </cdk-step>
</div>

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

@angular/material 7.0.2
@angular/cdk 7.0.2

[crisbeto]

I couldn't reproduce the issue based off of the code snippet above. Can you provide a more complete example?

[josephperrott]

Can you provide a reproduction in StackBlitz. This will help us to investigate the issue you are seeing.

Sorry about that. I am able to reproduce here.
https://stackblitz.com/edit/angular-material2-issue-68xhyx

[crisbeto]

@brackio your example seems to be on Material 6.0.0-beta.7. I can't reproduce it against 7.0.

How about this one? I updated the packages.

https://stackblitz.com/edit/angular-2dobc6

@crisbeto I updated the example. See above.

[crisbeto]

I can definitely see the error in the Stackblitz, but I'm having a hard time reproducing it in our dev app. The error comes from the ngAfterViewInit hook where the _stepHeader is undefined for some reason. This shouldn't be possible, because Angular defines it as a QueryList even if no elements match the query. The only case where it could be undefined is if we were checking it too early, however we're doing it in ngAfterViewInit which comes after ngAfterContentInit which is where the _stepHeader would be available.

[tobang]

I think this is related to #10614

[devversion]

I updated the StackBlitz to the latest version and this error no longer shows up. I also updated the StackBlitz to actually render the selected tab. Works as expected.

https://stackblitz.com/edit/angular-2dobc6?file=src%2Fapp%2Fapp.component.html