Sass generate content with white square?

Question

css

Hello!
Why does Sass compile this white square instead of "\f13"?

I use the built-in File Watcher PhpStorm.
I tried to test it on sassmeister.com
The result is the same:

Answer 1

https://github.com/sass/sass/issues/659
Works like this:
content: unquote("\"\\f13\"")