MdTooltip null reference property 'isVisible' on ESC key press

[TishchenkoAlex]

Bug, feature request, or proposal:

Bug

What is the expected behavior?

no error in console

What is the current behavior?

error in console

Cannot read property 'isVisible' of null
at MdTooltip._handleKeydown

line 276 from tooltip.ts
/** Handles the keydown events on the host element. */ _handleKeydown(e: KeyboardEvent) { if (this._tooltipInstance!.isVisible() && e.keyCode === ESCAPE) { e.stopPropagation(); this.hide(0); } }

What are the steps to reproduce?

http://plnkr.co/edit/8fIEmoi4IkPWSycODZ5R?p=preview

What is the use-case or motivation for changing an existing behavior?

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

Angular 4.3.6
Material beta 10
TS 2.5

Is there anything else we should know?

[angular-automatic-lock-bot]

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