Prevent undefined hint when minLength:0 focus

Resolves this onFocus bug which prints 'undefined' because `minLength:0`

before:
![image](https://cloud.githubusercontent.com/assets/906846/3362332/99612326-fb08-11e3-9f48-f1ea92bbcc66.png)

after:
![image](https://cloud.githubusercontent.com/assets/906846/3362361/c6f17b42-fb08-11e3-8582-ea7bbac86fe7.png)