I have a Maven plugin which works fine in standalone mvn 3.3.9 but throws a NPE if run via Jenkins maven-plugin.

Maven added a new property multiModuleProjectDirectory in 3.3.1 via this commit: https://git-wip-us.apache.org/repos/asf?p=maven.git;a=commitdiff;h=e28be4d33a0c2a1e4baeba56faace665804dfb60

The same property is missing in https://github.com/jenkinsci/maven-interceptors/blob/master/maven33-interceptor/src/main/java/org/apache/maven/cli/DefaultMavenExecutionRequestBuilder.java which in large parts is a copy of MavenCli.java. So please apply the changes from the first commitdiff link to DefaultMavenExecutionRequestBuilder.java. This seems to be somehow related to JENKINS-30460.