fix(ManageTripTracking): Use profile of primary traveler.

src/main/java/org/opentripplanner/middleware/models/MonitoredTrip.java

@@ -489,6 +489,14 @@ public static TripUsers getAddedUsers(MonitoredTrip monitoredTrip, MonitoredTrip
         return new TripUsers(addedPrimaryTraveler, addedCompanion, addedObservers);
     }
 
+    /**
+     * @return The id of the primary traveler (the primary user of a trip,
+     * or the user who created the trip if no primary user has been set).
+     */
+    public String getPrimaryTravelerId() {
+        return primary != null ? primary.userId : userId;
+    }
+
     public static class TripUsers {
         public final RelatedUser companion;
         public final List<RelatedUser> observers;

src/main/java/org/opentripplanner/middleware/triptracker/ManageTripTracking.java

@@ -89,7 +89,7 @@ private static TrackingResponse doUpdateTracking(Request request, TripTrackingDa
                 TripActions.getDefault().handleSegmentAction(
                     ((SelfLegInstruction)instruction).getLegStep(),
                     travelerPosition.expectedLeg.steps,
-                    Persistence.otpUsers.getById(tripData.trip.userId)
+                    Persistence.otpUsers.getById(tripData.trip.getPrimaryTravelerId())
                 );
             }
 

src/test/java/org/opentripplanner/middleware/models/MonitoredTripTest.java

@@ -150,4 +150,36 @@ private static Stream<Arguments> createGetAddedUsersCases() {
             )
         );
     }
+
+    @ParameterizedTest
+    @MethodSource("createGetPrimaryTravelerCases")
+    void canGetPrimaryTraveler(MobilityProfileLite primary, String creatorId, String expectedId, String message) {
+        MonitoredTrip trip = new MonitoredTrip();
+        trip.userId = creatorId;
+        trip.primary = primary;
+
+        assertEquals(expectedId, trip.getPrimaryTravelerId(), message);
+    }
+
+    private static Stream<Arguments> createGetPrimaryTravelerCases() {
+        final String creatorId = "creator-user-id";
+
+        MobilityProfileLite primary = new MobilityProfileLite();
+        primary.userId = "primary-user-id";
+
+        return Stream.of(
+            Arguments.of(
+                primary,
+                creatorId,
+                primary.userId,
+                "Should return the id of primary if it was set."
+            ),
+            Arguments.of(
+                null,
+                creatorId,
+                creatorId,
+                "Should return the id of the user that created the trip if primary is null."
+            )
+        );
+    }
 }