:style with value 0 ignored

[paulpflug]

Related to #3816

Vue.js version

2.0.1

Steps to reproduce

I having problems with reproducing on jsfiddle, and even in my projects it is inconsistent:

<div v-bind:style="style"></div>

data: ->
  style:
    top: 0

What is Expected?

div to have style="top:0px"

What is actually happening?

no top property in style

when I add this.style.left=0 at runtime it shows up - but on rerender it is missing again
Vue inspector also shows style.right=0

as a string it works as expected:

data: ->
  style:
    top: "0"