thanpolas/grunt-closure-tools — pull request #11 by scottlangendyk (2012-12-06 16:00:30+00:00)
Title: DepsWriter outputs to a file named 'undefined' if configured 'output_file' does not exist

Not an ideal solution, but it works.

A better solution would be to prepend the base path of the grunt project directory to the 'output_file' variable. However I'm not familiar with the Grunt API and couldn't find a documented way of doing that.