mishoo/UglifyJS2 — pull request #457 by dankohn (2014-03-27 14:11:43+00:00)
Title: Convert undefined files to empty string

This is a fix for https://github.com/mishoo/UglifyJS2/issues/456

This is a subtle and hard-to-replicate bug, but the fix is unlikely to have any negative consequences, since the function obviously fails if `files` is undefined.