[rules-users] [Error: incompatible types in statement: boolean (compared from: class be.axi.planner.domain.Task)]

I am using Drools Planner 5.5.0.Final. During the running of a unit test I sometimes get a crash with stack-trace shown beneath. It does not happen all the time, just now and then. But if it happens the process terminates and no solution is reached. Any ideas on this? The stack-trace does not show a lot on which rule is failing... [Error: incompatible types in statement: boolean (compared from: class be.axi.planner.domain.Task)] [Near : {... this == lead ....}]              ^ [Line: 1, Column: 1]     at org.mvel2.ast.BinaryOperation.<init>(BinaryOperation.java:84)     at org.mvel2.util.CompilerTools.finalizePayload(CompilerTools.java:118)     at org.mvel2.compiler.ExpressionCompiler._compile(ExpressionCompiler.java:287)     at org.mvel2.compiler.ExpressionCompiler.compile(ExpressionCompiler.java:62)     at org.mvel2.MVEL.compileExpression(MVEL.java:810)     at org.drools.base.mvel.MVELCompilationUnit.compile(MVELCompilationUnit.java:435)     at org.drools.base.mvel.MVELCompilationUnit.getCompiledExpression(MVELCompilationUnit.java:238)     at org.drools.rule.constraint.MvelConstraint.createMvelConditionEvaluator(MvelConstraint.java:206)     at org.drools.rule.constraint.MvelConstraint.evaluate(MvelConstraint.java:190)     at org.drools.rule.constraint.MvelConstraint.isAllowed(MvelConstraint.java:157)     at org.drools.reteoo.AlphaNode.assertObject(AlphaNode.java:137)     at org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:497)     at org.drools.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:382)     at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:235)     at org.drools.reteoo.EntryPointNode.assertObject(EntryPointNode.java:240)     at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:350)     at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:311)     at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:903)     at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:847)     at org.drools.planner.core.score.director.drools.DroolsScoreDirector.afterEntityAdded(DroolsScoreDirector.java:103)     at org.drools.planner.core.heuristic.selector.variable.PlanningVariableWalker.moveIterator(PlanningVariableWalker.java:145)     at org.drools.planner.core.constructionheuristic.greedyFit.decider.DefaultGreedyDecider.decideNextStep(DefaultGreedyDecider.java:74)     at org.drools.planner.core.constructionheuristic.greedyFit.DefaultGreedyFitSolverPhase.solve(DefaultGreedyFitSolverPhase.java:65)     at org.drools.planner.core.solver.DefaultSolver.runSolverPhases(DefaultSolver.java:190)     at org.drools.planner.core.solver.DefaultSolver.solve(DefaultSolver.java:155)     at be.axi.planner.app.InspectionSchedule.solve(InspectionSchedule.java:192)     at be.axi.planner.testcore.AbstractPlanningTestClass.solve(AbstractPlanningTestClass.java:288)     at be.axi.planner.testcore.AbstractPlanningTestClass.solve(AbstractPlanningTestClass.java:298)     at be.axi.planner.testcore.AbstractPlanningTestClass.solve(AbstractPlanningTestClass.java:315)     at be.axi.planner.TaskGroupingTest.communitySuccess02(TaskGroupingTest.java:289)     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)     at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)     at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)     at java.lang.reflect.Method.invoke(Unknown Source)     at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)     at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)     at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)     at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)     at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)     at org.junit.runners.BlockJUnit4ClassRunner.runNotIgnored(BlockJUnit4ClassRunner.java:79)     at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:71)     at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49)     at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)     at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)     at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)     at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)     at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)     at org.junit.runners.ParentRunner.run(ParentRunner.java:236)     at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)     at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)     at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)   ----------------- http://www.codessentials.com - Your essential software, for free! 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