Rethinking that line, checking if `this` is an instance of Y.Widget is a little over-cautious.  ButtonCore inherits from AttributeCore, so it will always have a `get` method, so falling into the condition can't result in a script error.  If the instance is a Widget, `get('boundingBox')` will return the node, if not, it will return `undefined`, which was already the value of `this._host` going into the branch.  Update coming.