Renderer.setElementAttribute's attributeValue parameter and strictNullChecks

[Dema]

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[x] feature request
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Current behavior
This is more a stylistic thing, but

this.renderer.setElementAttribute(this.el.nativeElement, 'data-some-param', undefined);

is a legal usage as it deletes data-some-param attribute from element, but this code shows typescript error when using strictNullChecks because setElementAttribute is described as:

abstract setElementAttribute(renderElement: any, attributeName: string, attributeValue: string): void;

attributeValue is just string and not string | undefined

Expected behavior

attributeValue to have type string | undefined
Minimal reproduction of the problem with instructions

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

Please tell us about your environment:

• Angular version: 2.2.4

https://github.com/angular/angular/blob/master/modules/%40angular/core/src/render/api.ts
still the same in latest Angular

• Browser: [all | Chrome XX | Firefox XX | IE XX | Safari XX | Mobile Chrome XX | Android X.X Web Browser | iOS XX Safari | iOS XX UIWebView | iOS XX WKWebView ]

• Language: [all | TypeScript X.X | ES6/7 | ES5]

• Node (for AoT issues): node --version =

[DzmitryShylovich]

Duplicate of #11844

[pkozlowski-opensource]

Closing as a duplicate of #11844, thnx @DzmitryShylovich

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