When Layout.regions is not set (and eg. initialized dynamically in initialize method), Layout.constructor -> Layout.initializeRegions throws an error in _.each because of Underscore 1.4 doesn't handle undefined values as empty object.
allow a layout to be defined without regions, using underscore v1.4.x…
…. fixes #270
thanks for noticing that! i had upgraded the test suite to underscore v1.4.1 already, but didn't have a test in place to check a layout that didn't have a regions defined on it. fixed and in the dev branch now.