[rules-users] Error selecting order decrease

Hello there, i'm getting this error: ------------------- 11:26:50.394 [main] INFO o.d.p.core.solver.DefaultSolver - Solving started: time spend (187), score (null), new best score (null), random seed (0). Exception in thread "main" java.lang.IllegalStateException: The selectionOrder (DECREASING_DIFFICULTY) can not be used on a PlanningEntity (com.swa.planner.domain.CloudProcess) that has no support for difficulty sorting. Check the @PlanningEntity annotation. at org.drools.planner.core.heuristic.selector.entity.PlanningEntitySelector.validate(PlanningEntitySelector.java:53) at org.drools.planner.core.heuristic.selector.entity.PlanningEntitySelector.phaseStarted(PlanningEntitySelector.java:45) at org.drools.planner.core.constructionheuristic.greedyFit.selector.GreedyPlanningEntitySelector.phaseStarted(GreedyPlanningEntitySelector.java:41) at org.drools.planner.core.constructionheuristic.greedyFit.DefaultGreedyFitSolverPhase.phaseStarted(DefaultGreedyFitSolverPhase.java:111) at org.drools.planner.core.constructionheuristic.greedyFit.DefaultGreedyFitSolverPhase.solve(DefaultGreedyFitSolverPhase.java:57) at org.drools.planner.core.solver.DefaultSolver.runSolverPhases(DefaultSolver.java:190) at org.drools.planner.core.solver.DefaultSolver.solve(DefaultSolver.java:155) at com.swa.planner.domain.CloudTest.main(CloudTest.java:51) ------------------------- I know why it is happening though (at least i think so), but will I have to implement the comparator to every planner I do or is there any other way to make it work? I'm reproducing the example from the guide, when it passes the drools rules it gives that message. I didn't implement CloudComputerStrengthComparator neither CloudProcessDifficultyComparator, will I have to implement those so this example works?