package.json file is not available after a fresh spark installation

I'm new to spark and I've just tried to follow the demo: https://laracasts.com/series/laravel-spark to start on, but after the installer asked: "Would you like to install the NPM dependencies? (yes/no) [yes]" a warning message appeared:

npm WARN enoent ENOENT: no such file or directory, open '****Sites/demo/package.json'

which leads to an error compiling assets: npm ERR! path */Sites/demo/package.json npm ERR! code ENOENT npm ERR! errno -2 npm ERR! syscall open npm ERR! enoent ENOENT: no such file or directory, open '/Sites/demo/package.json'

I have node -v: v7.7.4 npm -v: 4.4.4

am i missing anything ?