[rules-users] NPE at distribution [Planner]

Hello, I am getting an NPE when trying to solve a simple problem with 3 workorder and 3 engineers. ------------ Exception in thread "main" java.lang.NullPointerException at java.util.ArrayList.addAll(Unknown Source) at org.drools.planner.core.domain.solution.SolutionDescriptor.getAllFacts(SolutionDescriptor.java:178) at org.drools.planner.core.score.director.drools.DroolsScoreDirector.getWorkingFacts(DroolsScoreDirector.java:88) at org.drools.planner.core.score.director.drools.DroolsScoreDirector.resetWorkingMemory(DroolsScoreDirector.java:81) at org.drools.planner.core.score.director.drools.DroolsScoreDirector.setWorkingSolution(DroolsScoreDirector.java:70) at org.drools.planner.core.solver.scope.DefaultSolverScope.setWorkingSolutionFromBestSolution(DefaultSolverScope.java:158) at org.drools.planner.core.solver.DefaultSolver.solvingStarted(DefaultSolver.java:176) at org.drools.planner.core.solver.DefaultSolver.solve(DefaultSolver.java:154) at com.swa.planner.snap1.app.SortWorkOrder.main(SortWorkOrder.java:41) ----------------- the rule for it is simple (adapted from cloudbalancing): ---------- rule "requiredWorkTimeTotal" when $engineer : Engineer($worktime : worktime ) $requiredEngineerWorktimeTotal : Number(intValue > $worktime) from accumulate( WorkOrder( engineer == $engineer, $requiredWorktime : requiredWorktime ), sum($requiredWorktime) ) then insertLogical(new IntConstraintOccurrence("requiredWorkTimeTotal", ConstraintType.NEGATIVE_HARD, $requiredEngineerWorktimeTotal.intValue() - $worktime, $engineer)); end ---------- I'm rebuilding the app bit by bit and then evolve it. The skill is not considered yet to make the comparison, just worktime. This is the data i'm working with right now: ----------- List<Engineer> engineerList = new ArrayList<Engineer>(); engineerList.add(new Engineer(1l, 8, ABC1, "Fabio")); engineerList.add(new Engineer(2l, 8, ABC2, "Qwert")); engineerList.add(new Engineer(3l, 8, ABC3, "Trewq")); List<WorkOrder> workOrderList = new ArrayList<WorkOrder>(); workOrderList.add(new WorkOrder(101l, 8, ABC1)); workOrderList.add(new WorkOrder(102L, 8, ABC2)); workOrderList.add(new WorkOrder(103L, 8, ABC3)); -----------