Cannot call method 'slice' of undefined

[jpeterson]

I'm getting this output as a warning when running grunt. It's accompanied by a deprecation notice:

Running "autoprefixer:dist" (autoprefixer) task
Method autoprefixer.compile is deprecated and will be removed in 0.7 version. 
Use autoprefixer(reqs).compile instead.
Warning: Cannot call method 'slice' of undefined Used --force, continuing.

I'm not sure how to fix this. Here is the autoprefixer task in my Gruntfile:

autoprefixer: {
    dist: {
        options: {
            browsers: ['last 1 version']
        },
        files: [{
            expand: true,
            cwd: '.tmp/styles/',
            src: '{,*/}*.css',
            dest: '.tmp/styles/'
        }]
    }
},

[nDmitry]

Seems like you have new version of Autoprefixer (with new API), but the old one (0.1.x) of grunt-autoprefixer. Just upgrade the plugin.

[jpeterson]

Thanks for the quick response @nDmitry ... You were correct that I had the old version of grunt-autoprefixer. I've updated that and it gets rid of the deprecation warning... but I'm still getting the other one:

Running "autoprefixer:dist" (autoprefixer) task
Warning: Cannot call method 'slice' of undefined Use --force to continue.

[nDmitry]

Are you sure that your CSS is correct? Can you paste it somewhere? I'd try to reproduce the error.

[jpeterson]

The Sass file is here: https://github.com/jpeterson/yeoman-sandbox/blob/master/app/styles/main.scss

In fact, cloning that repo and following the instruction in the README will reproduce the error

[nDmitry]

I can't reproduce the error with your settings and file structure both on node 0.10 & 0.8, sorry. This the prefixed output: http://pastebin.com/7GAm4SXV

[jpeterson]

Thanks for taking a look... I'll continue troubleshooting and update here if I uncover the issue.