spring-cloud-function Kotlin functions aren't detected as expected

Describe the bug I'm fairly certiain this is something I've done wrong, but I can't see where.

The docs suggest that this should work:

@SpringBootApplication
class FunctionalApp {

    @Bean
    fun kotlinFunction(): (String) -> String {
        return { it.toUpperCase() }
    }
}

However, the function isn't registered. Hitting /actuator/functions returns:

{
  "functionRouter": {
    "type": "FUNCTION",
    "input-type": "object",
    "output-type": "object"
  }
}

If I move the registration into Java, it works as expected:

@Configuration
public class FunctionalConfig {
    @Bean
    public Function<String, String> uppercase() {
        return input -> input.toUpperCase();
    }
}

Now, hitting /actuator/functions returns:

{
  "functionRouter": {
    "type": "FUNCTION",
    "input-type": "object",
    "output-type": "object"
  },
  "uppercase": {
    "type": "FUNCTION",
    "input-type": "string",
    "output-type": "string"
  }
}

Sample This issue was detected as part of a broader project, which has a number of issues associated with it. There's a reproducable example showing this example here - specifically note that kotlinFunction isn't registered.