How to reproduce:
- Git clone optaplanner master
- Open projectJobSchedulingSolverConfig.xml.
- Comment out the <incrementalScoreCalculatorClass> element
- Comment in the <scoreDrl> element
- Run ProjectJobSchedulingApp and open dataset A-1.xml.


Stacktrace:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at org.drools.core.reteoo.BetaMemory.linkNode(BetaMemory.java:94)
at org.drools.core.reteoo.SingleObjectSinkAdapter.staticDoLinkRiaNode(SingleObjectSinkAdapter.java:100)
at org.drools.core.reteoo.SingleObjectSinkAdapter.doLinkRiaNode(SingleObjectSinkAdapter.java:83)
at org.drools.core.reteoo.RiaPathMemory.doLinkRule(RiaPathMemory.java:25)
at org.drools.core.reteoo.PathMemory.linkSegment(PathMemory.java:82)
at org.drools.core.reteoo.SegmentMemory.notifyRuleLinkSegment(SegmentMemory.java:177)
at org.drools.core.reteoo.SegmentMemory.linkNode(SegmentMemory.java:144)
at org.drools.core.reteoo.BetaMemory.linkNode(BetaMemory.java:94)
at org.drools.core.reteoo.BetaNode.assertObject(BetaNode.java:307)
at org.drools.core.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:502)
at org.drools.core.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:387)
at org.drools.core.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:294)
at org.drools.core.reteoo.EntryPointNode.assertObject(EntryPointNode.java:260)
at org.drools.core.common.NamedEntryPoint.insert(NamedEntryPoint.java:359)
at org.drools.core.common.NamedEntryPoint.insert(NamedEntryPoint.java:278)
at org.drools.core.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:1127)
at org.drools.core.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:1071)
at org.drools.core.impl.StatefulKnowledgeSessionImpl.insert(StatefulKnowledgeSessionImpl.java:285)
at org.optaplanner.core.impl.score.director.drools.DroolsScoreDirector.resetKieSession(DroolsScoreDirector.java:89)
at org.optaplanner.core.impl.score.director.drools.DroolsScoreDirector.setWorkingSolution(DroolsScoreDirector.java:76)
at org.optaplanner.examples.common.business.SolutionBusiness.openSolution(SolutionBusiness.java:230)
at org.optaplanner.examples.common.swingui.SolverAndPersistenceFrame$QuickOpenAction.actionPerformed(SolverAndPersistenceFrame.java:201)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3312)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:735)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:694)
at java.awt.EventQueue$3.run(EventQueue.java:692)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:708)
at java.awt.EventQueue$4.run(EventQueue.java:706)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:705)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)