grunt-cssmin banner not working

Question

Im using gruntjs/grunt-contrib-cssmin to minify & concat my css files, I wanted to add simple banner on my output css file, but its not working

  cssmin : {    
     distribute : {
       options: {
          banner: 'MY BANNER '
       },

       files: {
         'style.css' : ['src/css/empty.css']
       }
     }
  },

and output is body{background-color:#ff0}.... But expected output MY BANNER body{background-color:#ff0}