Can't run Pinger example

I cloned the jvm-libp2p and attempt to run the Pinger example by

  1. Compile by gradle clean build
  2. Run example by gradle run

with build.gradle.kts having following content added

plugins {
    application
    ...
}
application {
    mainClassName = "io.libp2p.example.ping.Pinger"
}

The result shows that

$ gradle run

> Task :run FAILED
Error: Could not find or load main class io.libp2p.example.ping.Pinger
Caused by: java.lang.ClassNotFoundException: io.libp2p.example.ping.Pinger

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':run'.
> Process 'command '/home/jason/jdk-11.0.6+10/bin/java'' finished with non-zero exit value 1

Note that the source code Pinger.java is coded with package io.libp2p.example. But neither using io.libp2p.example.ping.Pinger nor io.libp2p.example.Pinger in build.gradle.ktsapplication section would work (regardless whether the package name in Pinger.java is package io.libp2p.example.ping or package io.libp2p.example.

Any suggestion? Thanks