How can I get all Kotlin file in a `Project`?

I want to get all the declarations and references in a mixed Java-Kotlin project, but when I create a project according to the test case I saw in the kotlin repo, I can only get java’s psi classes/files.

I tried resolving some Java code that calling Kotlin, I get null (but I can resolve Java codes calling Java).

Plus, I can get Java’s PsiClass using APIs like But I cannot get Kotlin’s org.jetbrains.kotlin.psi.KtClass by the same API. Am I missing something?