Fix NullPointerException when searching backwards with a frequency-based trip

application/src/main/java/org/opentripplanner/routing/algorithm/raptoradapter/transit/frequency/TripFrequencyAlightSearch.java

@@ -60,6 +60,6 @@ public RaptorBoardOrAlightEvent<T> search(
         }
       }
     }
-    return null;
+    return RaptorBoardOrAlightEvent.empty(earliestBoardTime);
   }
 }

application/src/test/java/org/opentripplanner/routing/algorithm/raptoradapter/transit/request/TripPatternForDatesTest.java

@@ -0,0 +1,119 @@
+package org.opentripplanner.routing.algorithm.raptoradapter.transit.request;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.time.LocalDate;
+import java.util.BitSet;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+import org.opentripplanner.model.Frequency;
+import org.opentripplanner.model.StopTime;
+import org.opentripplanner.raptor.api.model.SearchDirection;
+import org.opentripplanner.routing.algorithm.raptoradapter.transit.TripPatternForDate;
+import org.opentripplanner.transit.model._data.TimetableRepositoryForTest;
+import org.opentripplanner.transit.model.framework.Deduplicator;
+import org.opentripplanner.transit.model.network.Route;
+import org.opentripplanner.transit.model.network.RoutingTripPattern;
+import org.opentripplanner.transit.model.network.StopPattern;
+import org.opentripplanner.transit.model.network.TripPattern;
+import org.opentripplanner.transit.model.timetable.FrequencyEntry;
+import org.opentripplanner.transit.model.timetable.TripTimes;
+import org.opentripplanner.transit.model.timetable.TripTimesFactory;
+
+class TripPatternForDatesTest {
+
+  private static final int FREQUENCY_START = 7 * 60 * 60;
+  private static final int FREQUENCY_END = 23 * 60 * 60;
+  private static final int HEADWAY = 300;
+  private static final Route ROUTE = TimetableRepositoryForTest.route("1").build();
+  private static final LocalDate SERVICE_DATE = LocalDate.of(2024, 11, 1);
+
+  @Test
+  void forwardSearchInRange() {
+    var result = getTestSubjectWithExactFrequency()
+      .createCustomizedTripSearch(SearchDirection.FORWARD)
+      .search(FREQUENCY_END - HEADWAY, 0);
+    assertTrue(result.time() >= FREQUENCY_END - HEADWAY);
+    assertTrue(result.time() < FREQUENCY_END);
+  }
+
+  @Test
+  void forwardSearchOutOfRange() {
+    var result = getTestSubjectWithExactFrequency()
+      .createCustomizedTripSearch(SearchDirection.FORWARD)
+      .search(FREQUENCY_END, 0);
+    assertTrue(result.empty());
+  }
+
+  @Test
+  void reverseSearchInRange() {
+    var result = getTestSubjectWithExactFrequency()
+      .createCustomizedTripSearch(SearchDirection.REVERSE)
+      .search(FREQUENCY_START, 0);
+    assertEquals(FREQUENCY_START, result.time());
+  }
+
+  @Test
+  void reverseSearchOutOfRange() {
+    var result = getTestSubjectWithExactFrequency()
+      .createCustomizedTripSearch(SearchDirection.REVERSE)
+      .search(FREQUENCY_START - 1, 0);
+    assertTrue(result.empty());
+  }
+
+  private static TripPatternForDates getTestSubjectWithExactFrequency() {
+    var testModel = TimetableRepositoryForTest.of();
+    var stop1 = testModel.stop("FEED:STOP1", 0, 0).build();
+    var stop2 = testModel.stop("FEED:STOP2", 0, 0).build();
+
+    var stopTime1 = new StopTime();
+    stopTime1.setStop(stop1);
+    stopTime1.setArrivalTime(0);
+    stopTime1.setDepartureTime(0);
+    stopTime1.setStopSequence(0);
+    var stopTime2 = new StopTime();
+    stopTime2.setStop(stop2);
+    stopTime2.setArrivalTime(300);
+    stopTime2.setDepartureTime(300);
+    stopTime2.setStopSequence(1);
+    StopPattern stopPattern = new StopPattern(List.of(stopTime1, stopTime2));
+    RoutingTripPattern tripPattern = TripPattern
+      .of(TimetableRepositoryForTest.id("P1"))
+      .withRoute(ROUTE)
+      .withStopPattern(stopPattern)
+      .build()
+      .getRoutingTripPattern();
+
+    final TripTimes tripTimes = TripTimesFactory.tripTimes(
+      TimetableRepositoryForTest.trip("1").withRoute(ROUTE).build(),
+      List.of(stopTime1, stopTime2),
+      new Deduplicator()
+    );
+
+    var frequency = new Frequency();
+    frequency.setStartTime(FREQUENCY_START);
+    frequency.setEndTime(FREQUENCY_END);
+    frequency.setHeadwaySecs(HEADWAY);
+    frequency.setExactTimes(1);
+
+    var boardingAndAlightingPossible = new BitSet(2);
+    boardingAndAlightingPossible.set(0);
+    boardingAndAlightingPossible.set(1);
+
+    return new TripPatternForDates(
+      tripPattern,
+      new TripPatternForDate[] {
+        new TripPatternForDate(
+          tripPattern,
+          List.of(tripTimes),
+          List.of(new FrequencyEntry(frequency, tripTimes)),
+          SERVICE_DATE
+        ),
+      },
+      new int[] { 0 },
+      boardingAndAlightingPossible,
+      boardingAndAlightingPossible,
+      0
+    );
+  }
+}