Is it possible to use ProGuard with Kotlin?

I am just wondering since I haven't managed to be able to eliminate the ProGuard error such as

[AndroidRivers] Warning: com.silverkeytech.android_rivers.CacheItem: can’t find referenced class

But again I am a totally newbie on this.

It is a bug:

Thanks for the report

BTW, you can supress a proguard warning by saying something like