No platforms added to this project

[julkue]

After running $ grunt phonegap:build I get the following error:

My grunt task:

phonegap: {
    config: {
        root: 'dist/tmp/',
        config: 'phonegap/config.xml',
        cordova: 'phonegap/.cordova',
        path: 'phonegap-build/',
        platforms: ['android'],
        cleanBeforeBuild: true
    }
}

What is the reason? As you can see I have added the platforms array correctly.