Not exactly sure if these are truly needed, but J-on-J otherwise fails with compilation error.

It's apparently failing to properly deduce the JobT type. Making it explicit to avoid stretching the compiler

core/src/main/java/hudson/model/Run.java

@@ -1408,11 +1408,11 @@ public abstract class Run <JobT extends Job<JobT,RunT>,RunT extends Run<JobT,Run
          */
         public abstract void cleanUp(BuildListener listener) throws Exception;
 
-        public final RunT getBuild() {
+        public RunT getBuild() {
             return _this();
         }
 
-        public final JobT getProject() {
+        public JobT getProject() {
             return _this().getParent();
         }
     }

maven-plugin/src/main/java/hudson/maven/MavenBuild.java

@@ -644,6 +644,16 @@ public class MavenBuild extends AbstractMavenBuild<MavenModule,MavenBuild> {
     private class MavenBuildExecution extends AbstractBuildExecution {
         private List<MavenReporter> reporters;
 
+        @Override
+        public MavenBuild getBuild() {
+            return (MavenBuild)super.getBuild();
+        }
+
+        @Override
+        public MavenModule getProject() {
+            return (MavenModule)super.getProject();
+        }
+
         @Override
         protected Lease decideWorkspace(Node n, WorkspaceList wsl) throws InterruptedException, IOException {
             return wsl.allocate(getModuleSetBuild().getModuleRoot().child(getProject().getRelativePath()));