code: @Override
  	protected void checkPrimitiveValidity() {
  		BusPrimitiveInvalidity invalidityReason = null;
  		if (this.busStops.isEmpty()) {
  			invalidityReason = new BusPrimitiveInvalidity(
  					BusPrimitiveInvalidityType.NO_STOP_IN_HUB,
  					null);
  		} else {
  			final Iterator<BusStop> iterator = this.busStops.iterator();
  			while (iterator.hasNext() && invalidityReason == null) {
  				final BusStop stop = iterator.next();
  				if (!stop.isValidPrimitive()) {
  					invalidityReason = new BusPrimitiveInvalidity(
  							BusPrimitiveInvalidityType.INVALID_LINKED_STOP,
  							stop.getName());
  				} else {
  					final BusNetwork bn = stop.getBusNetwork();
  					if (bn == null || bn != getBusNetwork()) {
  						invalidityReason = new BusPrimitiveInvalidity(
  								BusPrimitiveInvalidityType.NOT_IN_SAME_NETWORK,
  								null);
  					}
  				}
  			}
  		}
  		setPrimitiveValidity(invalidityReason);
  	}
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