fix: check if blockid is present

Author: cka-y

main/src/main/java/org/mobilitydata/gtfsvalidator/validator/InconsistentRouteTypeForBlockIdValidator.java

@@ -33,7 +33,7 @@ public void validate(NoticeContainer noticeContainer) {
         .asMap()
         .forEach(
             (blockId, trips) -> {
-              if (blockId != null) {
+              if (blockId != null && !blockId.isEmpty()) {
                 List<GtfsRouteType> routeTypes =
                     trips.stream()
                         .map(trip -> routeTable.byRouteId(trip.routeId()))