shadowJar minimize() removes all class files

Question

I'm using shadowJar in my Gradle-built Kotlin project and the fat jar it produces seems to work fine. When I enable minimization though, the produced jar has no class files in it.

Here's how it's configured.

plugins {
    id("com.github.johnrengelman.shadow") version "7.1.2"
}
//...
tasks.named("shadowJar", ShadowJar::class) {
    minimize()
}

This seems to be in line with the documented usage. Maybe my build.gradle.kts isn't properly declaring some entry point that shadowJar needs to decide that a class file is used?