angular/angular.js — pull request #7762 by rodyhaddad (2014-06-09 22:56:40+00:00)
Title: fix($parse): mark empty expressions as constants and literals

In response of [#1405 (comment)](https://github.com/angular/angular.js/issues/1405#issuecomment-45525863)

I decided to mark it as a literal because `$parse('undefined')` is a literal.