Module build failed: visitors[i].run is not a function

[Bnaya]

the main.less file is empty, and i'm getting:

ERROR in ./styles/main.less
Module build failed: visitors[i].run is not a function
 @ /Users/bnaya/dev/opensource/hasadna/open-budget-frontend/open-budget/app/styles/main.less (line null, column -1)
 near lines:



 @ ./scripts/main.coffee 3:2-29

less 1.7.5 installed

my webpack config:

loaders:
...
          {
            test: /\.less$/,
            loader: ExtractTextPlugin.extract('less?sourceMap')
          }
...
    plugins: [
      new webpack.ProvidePlugin({
          $: "jquery",
          jQuery: "jquery",
          "window.jQuery": "jquery"
      }),
      // new webpack.IgnorePlugin(/^\.\/lang$/),
      new ExtractTextPlugin('styles.css')
    ]