I tested this with Fedora OpenJDK11
{{[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary for Undertow 2.0.29.Final-SNAPSHOT:
[INFO]
[INFO] Undertow ........................................... SUCCESS [ 1.747 s]
[INFO] Undertow Parser Generator .......................... FAILURE [ 3.650 s]
[INFO] Undertow Core ...................................... SKIPPED
[INFO] Undertow Servlet ................................... SKIPPED
[INFO] Undertow WebSockets JSR356 implementations ......... SKIPPED
[INFO] Undertow Examples .................................. SKIPPED
[INFO] Undertow Karaf Features ............................ SKIPPED
[INFO] Undertow Benchmarks ................................ SKIPPED
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 5.723 s
[INFO] Finished at: 2020-01-04T05:48:56-03:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-javadoc-plugin:3.0.1:jar (attach-javadocs) on project undertow-parser-generator: MavenReportException: Error while generating Javadoc:
[ERROR] Exit code: 1 - javadoc: error - The code being documented uses modules but the packages defined in https://docs.oracle.com/javase/8/docs/api/ are in the unnamed module.
[ERROR]
[ERROR] Command line was: /usr/lib/jvm/java-11-openjdk/bin/javadoc @options @packages
[ERROR]
[ERROR] Refer to the generated Javadoc files in '/home/fla/Development/projects/undertow/parser-generator/target/apidocs' dir.
[ERROR]
[ERROR] -> [Help 1]
}}