v-attr behaving differently in 0.12.8

[gapipro]

So after last update v-attr is behaving differently then before.

Mostly this affects image loading.

For example when you load image like this

<img v-attr="src:demo.url" />

In previous version until demo.url was not set src attribute was not inserted into DOM.

But in latest version until demo.url is not set src attribute equals to undefined. That triggers image download on invalid url.

I know it can be fixed with v-if="demo.url" but previous syntax was much cleaner.

You can see this issue here: http://jsfiddle.net/v8g6csff/