Invalid Parameters Exception

When vendor.twbs.bootstrap.dist alias and cdnUrl are not set, Yii tries to publish the entire site and gets a PHP Warning.

copy(C:\sv\www\yiistrap-bs3\assets\f7a472d9\assets\f7a472d9\assets\f7a472d9\assets\f7a472d9\assets\f7a472d9\assets\f7a472d9\assets\f7a472d9\assets\f7a472d9\assets\f7a472d9\assets\f7a472d9\assets\f7a472d9\assets\d7f2a1\jui\css\base\images\ui-bg_flat_0_aaaaaa_40x100.png) [<a href='function.copy'>function.copy</a>]: failed to open stream: Invalid argument

I think Yiistrap should throw an Exception, allowing to realize what's wrong and prevent Yii from copying the whole site into assets.