angular/angular.js — pull request #7024 by lgalfaso (2014-04-07 04:13:49+00:00)
Title: fix(ngOption): accept `0` as an option group

Accept `0` and an option group

Close #7015

BREAKING CHANGE

When using option groups at an ng-option, the literal `0` will
be handled as a group with label `'0'`. Use the literal string `''`
or undefined for options that should not be in any option group