base_url() and site_url() in CI_3.0.3

Hello, I using site_url method for load css and js file in my app.



and today I up to CI_3.0.3, site_url is not working I can not load css and js file.

now I must set my domain in $config['base_url'] (not empty) and then site_url is working.

my question in CI_3.0.3 is : why site_url is not working and why I must set my domain in $config['base_url'] ?
(in CI_3.0.2 site_url method is working when $config['base_url'] is empty)

sorry, my eng is bad. thank you.