No error on empty selector

Steps to reproduce:
1. Create a new .css file. Using <fx:Style source="xxx.css"/> to import styles to the main application file.
2. The .css file have the following as content:
{
color:#aaaaaa;
}
3. Save the .css file

Actual Results:
No error reported.

Expected Results:
Report error because empty selector is invalid.

Workaround (if any):