Fatal error when running grunt on 0.3.x project

[Krinkle]

On a project with a grunt.js file from before the 0.4 upgrade (in this case an old branch of mine from jquery/jquery) running grunt (/usr/local/bin/grunt -> ../lib/node_modules/grunt-cli/bin/grunt) gives the following:

$ grunt
Fatal error: Object prototype may only be an Object or null

$ grunt --verbose
Initializing
Command-line options: --verbose

Reading "null" Gruntfile...ERROR
Fatal error: Object prototype may only be an Object or null

[cowboy]

I don't have any problem here running the 'grunt' command from grunt-cli inside a project where grunt 0.3.x has been installed locally.

[cowboy]

What version of grunt-cli are you using? Please make sure you're using the latest.

[Krinkle]

Using npm install -g grunt-cli@latest, and jquery/jquery right before it switched to Grunt 0.4.x.

I can no longer reproduce the error though.