Window.zoomLevel, wrong default value; in `Window.zoomLevel = <val>`, <val> needs to be a list??

When mucking about in the Developer tools console in empty node-webkit (started as just `$ nw`, I find:

````
> var gui = require('nw.gui');
  undefined
> var win = gui.Window.get();
  undefined
> win.zoomLevel
  0
````
According to the WebKit API, at least: http://webkitgtk.org/reference/webkitgtk/stable/webkitgtk-webkitwebview.html#WebKitWebView--zoom-level
this default value should be 1, I think.

Back to the Console:
````
> win.zoomLevel = 1.2;
  Error: Unable to convert 'args' passed to CallObjectMethodSync
```
From looking around the source code line where this error message is being produced:

[src/api/bindings_common.cc:149](../blob/master/src/api/bindings_common.cc)

I get that this function is expecting a list. Why a list and not a scalar number?

If I test in the Console:
````
> win.zoomLevel = [1.2];
````
and switch back to the main window, it appears setting the zoom level has indeed worked.

Back to the Console:
````
> win.zoomLevel
  1.2000000476837158
````
Besides the obvious binary rounding error, the vaue is correct, but is a scalar again.
What gives?