Bug - layertree

I've updated CGXP on SITN and I have a bug since then.

Firebug tells me that `styles is undefined` on line 337 of https://github.com/camptocamp/cgxp/blob/master/core/src/script/CGXP/widgets/tree/LayerTree.js

This line was inserted by commit https://github.com/caatmptocamp/cgxp/commit/622e2dc330ef1a69aa40fd7720f3f909093fa0a6

Could somebody check what's wrong and eventually propose a patch?