In some rare circumstances, looking up transit stops can fail when no walking route is found, this can be seen i.e. if running OTP with the Swedish data and doing a route search to/from the place Sjisjka. This is located far out in road-less land along Malmbanan (and the OSM mapping lacks walking paths and stuff in this area), so GraphHopper is unable to find an exact walking route (the code in openTripPlanner.js does such a search for stops that are more than 100 m from the search location in an "as the crow flies manner"). I'm not 100% sure of the best solution here, either just bail out and use the straight-line distance in these cases, or fail the routing request.