Cancelling a stop with GTFS-RT fails when the scheduled stop times are repeating

[leonardehrenfried]

If you have the following GTFS trip

stop	arrival	departure
A	10:00	10:01
B	10:01	10:01
C	10:01	10:02

which is a little odd but satisfies the GTFS spec and our internal constraints and apply a GTFS-RT trip update which SKIPs stop B, it fails with a NEGATIVE_HOP_TIME error.

That is because the stop cancellation logic assumes that the travel time between the stops is greater than zero:

OpenTripPlanner/application/src/main/java/org/opentripplanner/updater/trip/gtfs/DefaultForwardsDelayInterpolator.java

Lines 92 to 95 in f1d0f7b

	int prevScheduledDeparture = builder.getScheduledDepartureTime(firstCanceledStop - 1);
	int scheduledTravelTime = builder.getScheduledArrivalTime(i) - prevScheduledDeparture;
	int realTimeTravelTime = arrival - prevDeparture;
	double travelTimeRatio = (double) realTimeTravelTime / scheduledTravelTime;

If the travel time is zero, then travelTimeRatio becomes Infinity leading to validation errors.

cc @laurentg