Before, this worked:
<style>
.cls-1 {}
<!-- foo -->
.cls-2 {}
</style>

but this failed:
<style>
.cls-1 {} <!-- foo -->
.cls-2 {}
</style>

.cls-1 would be prefixed, but .cls-2 and subsquent classes would not.

The root cause is an empty return that was missed during a refactor to
switch from forEach() with a lambda to a for () loop.

Add a new test to cover this case.

Co-authored-by: Seth Falco <seth@falco.fun>