NullPointerException is thrown when forcing a process to end using ExecutionService.endProcessInstance(...) having attached end event listener

DefaultCommandService - exception while executing command org.jbpm.pvm.internal.cmd.EndProcessInstance@6649
java.lang.NullPointerException
at org.jbpm.pvm.internal.util.ReflectUtil.installDeploymentClassLoader(ReflectUtil.java:385)
at org.jbpm.pvm.internal.util.ReflectUtil.instantiateUserCode(ReflectUtil.java:412)
at org.jbpm.pvm.internal.wire.usercode.UserCodeReference.getObject(UserCodeReference.java:63)
at org.jbpm.pvm.internal.wire.usercode.UserCodeReference.getObject(UserCodeReference.java:47)
at org.jbpm.pvm.internal.wire.usercode.UserCodeEventListener.notify(UserCodeEventListener.java:38)
at org.jbpm.pvm.internal.model.op.ExecuteEventListener.perform(ExecuteEventListener.java:81)
at org.jbpm.pvm.internal.model.ExecutionImpl.performAtomicOperationSync(ExecutionImpl.java:672)
at org.jbpm.pvm.internal.model.ExecutionImpl.performAtomicOperation(ExecutionImpl.java:632)
at org.jbpm.pvm.internal.model.ExecutionImpl.fire(ExecutionImpl.java:579)
at org.jbpm.pvm.internal.model.ExecutionImpl.fire(ExecutionImpl.java:568)
at org.jbpm.pvm.internal.model.ExecutionImpl.end(ExecutionImpl.java:386)
at org.jbpm.pvm.internal.cmd.EndProcessInstance.execute(EndProcessInstance.java:48)
at org.jbpm.pvm.internal.svc.DefaultCommandService.execute(DefaultCommandService.java:42)
at org.jbpm.pvm.internal.svc.SkipInterceptor.execute(SkipInterceptor.java:40)
at org.jbpm.pvm.internal.svc.ExecutionServiceImpl.endProcessInstance(ExecutionServiceImpl.java:117)