Getting a NoClassDefFoundError when calling a kotlin extension function

Question

I'm using the Android Studio 3.0 Beta 2 Canary Preview, and am calling a Kotlin extension function from Java:

The Kotlin code:

fun Metadata.validate(context: Context) {
    validateInnerList(context)
    // other validation functions
}

private fun Metadata.validateInnerList(context: Context) {
    taskGroupList.removeIf { !it.isDataValid() } // error goes here
}

the java code:

metadataDecoratorKt.validate(metadata, context);

The code compiles fine, but during runtime calling it gives me a - java.lang.NoClassDefFoundError

Am I doing something wrong? is there an error on Intellij's side? If more information is needed please say so.