It cannot be empty. Otherwise, you will not be able to see anything. Because any theme loads all the styling from style.css and functions from functions.php (Basic theme)
If you’ve created a child theme, then child theme contents (Functions.php and style.css) should be empty.
Are you able to access your site?
The theme’s functions.php kicks off init.php, which in turn kicks off all the other processes. So it contains only that one line for itself.
The stylesheet is loaded programatically by other files. Depending on what skin you have chosen, the theme will load red.css, blue.css, etc.
If you want to make modifications, you should create a child theme and edit that. (See How to Customize Customizr for more.)
