NPE when using entitySelector with sorting and STEP cache type

Describe the bug
Using a sorted entitySelector with cacheType STEP causes a null pointer exception.

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.util.List.iterator()" because "this.cachedEntityList" is null
        at ai.timefold.solver.core.impl.heuristic.selector.entity.decorator.SortingEntitySelector.iterator(SortingEntitySelector.java:41)
        at ai.timefold.solver.core.impl.heuristic.selector.common.iterator.AbstractOriginalChangeIterator.<init>(AbstractOriginalChangeIterator.java:23)
        at ai.timefold.solver.core.impl.heuristic.selector.move.generic.ChangeMoveSelector$2.<init>(ChangeMoveSelector.java:101)
        at ai.timefold.solver.core.impl.heuristic.selector.move.generic.ChangeMoveSelector.iterator(ChangeMoveSelector.java:101)
        at ai.timefold.solver.core.impl.constructionheuristic.placer.PooledEntityPlacer$PooledEntityPlacingIterator.createUpcomingSelection(PooledEntityPlacer.java:30)
        at ai.timefold.solver.core.impl.constructionheuristic.placer.PooledEntityPlacer$PooledEntityPlacingIterator.createUpcomingSelection(PooledEntityPlacer.java:23)
        at ai.timefold.solver.core.impl.heuristic.selector.common.iterator.UpcomingSelectionIterator.hasNext(UpcomingSelectionIterator.java:27)
        at ai.timefold.solver.core.impl.constructionheuristic.DefaultConstructionHeuristicPhase.solve(DefaultConstructionHeuristicPhase.java:45)
        at ai.timefold.solver.core.impl.solver.AbstractSolver.runPhases(AbstractSolver.java:83)
        at ai.timefold.solver.core.impl.solver.DefaultSolver.solve(DefaultSolver.java:193)
        at testschedules.Main.main(Main.java:15)

To Reproduce

• Clone https://github.com/aioobe/timefold-repro-step-sorted-entities

• Run with

  ./gradlew -Dorg.gradle.java.home=/path/to/java17 run
  

Environment

Timefold Solver Version or Git ref: 1.0.0

Output of java -version:

java version "17.0.7" 2023-04-18 LTS
Java(TM) SE Runtime Environment (build 17.0.7+8-LTS-224)
Java HotSpot(TM) 64-Bit Server VM (build 17.0.7+8-LTS-224, mixed mode, sharing)

Output of uname -a or ver:

Linux xyz 5.15.0-76-generic #83~20.04.1-Ubuntu SMP Wed Jun 21 20:23:31 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

Additional information

I think the issue is the following:

1. DefaultConstructionHeuristicPhase.java:45 tries to start iterating over the entities
2. Since cacheType STEP is used, the cachedEntityList in SortingEntitySelector has not been initialized.
3. The cachedEntityList would have been initialized in DefaultConstructionHeuristicPhase.java:47, but that has obviously not been executed yet.

So there's a little chicken and egg situation.