Autocompleted mdInput with undefined ngModel shows "undefined" instead of empty text

[molcik]

Bug, feature request, or proposal:

bug

What is the expected behavior?

Autocompleted mdInput binded with undefined ngModel should display empty text instead of "undefined".

What is the current behavior?

Regular mdInput shows empty text in case of ngModel is undefined.
Autocompleted mdInput binded with undefined ngModel shows "undefined".

What are the steps to reproduce?

Here is the plunker with description
http://plnkr.co/edit/5jrByGdNel0saoQe7obm

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

All mdInput should behave consistently.

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

Tested with @angular/material 2.0.0-beta.2

Is there anything else we should know?

[angular-automatic-lock-bot]

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