Use of any webpack.config.coffee throws #1284

$ ls | grep webpack
webpack.config.coffee

$ webpack

assert.js:86
  throw new assert.AssertionError({
        ^
AssertionError: path must be a string
    at Module.require (module.js:364:3)
    at require (module.js:384:17)
    at module.exports (c:\Users\Kamil\AppData\Roaming\npm\node_modules\webpack\bin\convert-argv.js:61:19)
    at Object.<anonymous> (c:\Users\Kamil\AppData\Roaming\npm\node_modules\webpack\bin\webpack.js:54:40)
    at Module._compile (module.js:460:26)
    at Object.Module._extensions..js (module.js:478:10)
    at Module.load (module.js:355:32)
    at Function.Module._load (module.js:310:12)
    at Function.Module.runMain (module.js:501:10)
    at startup (node.js:129:16)