Adding plain kotlin module to android project

Question

I'm trying to add module to my android project. I'd like to add plain kotlin library (without any knowledge of android):

• I've created new android project
• clicked right click on project, New -> Module (on image it exists, but it's not a problem, I've created it before)

Then I'm trying to perform any operation on String in new module, but it ends up with error:

Please note that whole build completes successfully (./gradlew build). However android studio marks errors & refactoring is not possible. Invalidating cache & restart did not help.