Gulp not creating any files

I created a project for becoming familiar with build tools. My folder structure for this project looks like so:

my public folder

+ my-project
|-- + css
|----document
|------dropbox.css
|------dropbox.css.map
|----knowledgebase
|------knowledgebase.css
|------knowledgebase.map
|app.css
|app.css.map

my resources/assets/sass/ folder look like this

|-- + css
|----document
|------dropbox.scss
|----knowledgebase
|------knowledgebase.scss
|app.scss

when i tried to add the third event.scss and run gule no files is creating

|-- + css
|----document
|------dropbox.scss
|----knowledgebase
|------knowledgebase.scss
|----event
|-------event.scss
|app.scss

Here is my gulp files

var elixir = require('laravel-elixir');

elixir(function(mix) {
    mix.sass('app.scss', './public/css/app.css')
       .sass('document/dropbox.scss', './public/css/document/dropbox.css')
       .sass('knowledgebase/knowledgebase.scss', './public/css/knowledgebase/knowledgebase.css')
       .sass('event/event.scss', '.public/css/event/event.css');
    mix.version([
        'public/css/app.css',
        'public/css/document/dropbox.css',
        'public/css/knowledgebase/knowledgebase.css'
    ]);
    mix.scripts([
        'app.js',
        './public/js/all.js'
    ]);
});

The output has no errors

Fetching Sass Source Files...
   - resources/assets/sass/event/event.scss


Saving To...
   - .public/css/event/event.css

[11:19:16] gulp-notify: [Laravel Elixir] Sass Compiled!
[11:19:16] Finished 'sass' after 32 ms
[11:19:16] Starting 'version'...

at the end my public/css/event folder has no event.css any ideas would be great.Thank you