Ensure `attr` is a string when passed to `this.map`.
Ensure `attr` is a string when passed to `this.map`.

platinumazure/backbone,jridgewell/backbone,moimikey/backbone,lastjune/backbone,alekskorolev/lightbones,darrrk/backbone,akre54/backbone,alekskorolev/lightbones,lastjune/backbone,jashkenas/backbone,ppker/backbone,zgl2007dj/backbone,jridgewell/backbone,craigmichaelmartin/backbone,craigmichaelmartin/backbone,platinumazure/backbone,jashkenas/backbone,darrrk/backbone,zgl2007dj/backbone,moimikey/backbone,akre54/backbone,ppker/backbone