if you use the eclipse compiler to try and build core you see a lot of code failing to compile as there there are classes contained in 2 locations which is illegal (the javac compiler is allowing this - but I believe eclipse is correct in emmitting this error)

the biggest offender seems to be org.xml.sax.SAXException which is mostly coming from test cases (that use JenkinsRule.createWebClient()

the error is The package org.xml.sax is accessible from more than one module: <unnamed>, java.xml

This can be trivially fixed in test code by changing the throws `SAXException to throws EXception however this is not fixing the underlying issue where the classes are in 2 distinct jar files.

Steps to Reproduce

clone jenkinsci/jenkins
import the project into eclipse as a maven project (using m2e)

Expected results

The project imports and builds without issue
This was the case prior to java11 work

actual results

The project imports however has a slew of java compilation issues the majority of which are all about importing org.xml.sax.something or org.w3c.someting,

Note: this could possibly be reproduced by switching maven to use the eclipse compiler also. https://maven.apache.org/plugins/maven-compiler-plugin/non-javac-compilers.html