Starting with Java 9+, JAXB has been removed from the JDK. So it's a good thing to try and break/remove the dependency against from plugins who do not really use JAXB for its core feature (object de/serialization).
martinda please check the following pull request https://github.com/jenkinsci/job-import-plugin/pull/26
Fixed in jenkinsci/job-import-plugin#26. Released in 3.2.
martinda please check the following pull request https://github.com/jenkinsci/job-import-plugin/pull/26