Javadoc build fails on fresh checkout of master or rel/wicket-9.3.0

could be some kind of setup error, but mvn clean install with java 16.0.1 installed produces:

[ERROR] MavenReportException: Error while generating Javadoc:
Exit code: 1 - javadoc: error - invalid flag: --no-module-directoriesCommand line was: /Library/Java/JavaVirtualMachines/jdk-16.0.1.jdk/Contents/Home/bin/javadoc -J-Xmx256m -J-Xms128m --no-module-directories @options @packagesRefer to the generated Javadoc files in '/Users/jonathan/Workspaces/Wicket/wicket/wicket-request/target/apidocs' dir.org.apache.maven.reporting.MavenReportException:
Exit code: 1 - javadoc: error - invalid flag: --no-module-directoriesCommand line was: /Library/Java/JavaVirtualMachines/jdk-16.0.1.jdk/Contents/Home/bin/javadoc -J-Xmx256m -J-Xms128m --no-module-directories @options @packagesRefer to the generated Javadoc files in '/Users/jonathan/Workspaces/Wicket/wicket/wicket-request/target/apidocs' dir.