#vulnerable code 
                                @Override
    public double getActivityStartTime(TourActivity activity, double arrivalTime) {
        TimeWindow last = null;
        for(int i=activity.getTimeWindows().size()-1; i >= 0; i--){
            TimeWindow tw = activity.getTimeWindows().get(i);
            if(tw.getStart() <= arrivalTime && tw.getEnd() >= arrivalTime){
                return arrivalTime;
            }
            else if(arrivalTime > tw.getEnd()){
                if(last != null) return last.getStart();
                else return arrivalTime;
            }
            last = tw;
        }
        return Math.max(arrivalTime,last.getStart());
    } 
                            #location 15 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                @Override
    public double getActivityStartTime(TourActivity activity, double arrivalTime) {
        return Math.max(arrivalTime,activity.getTheoreticalEarliestOperationStartTime());
//        TimeWindow last = null;
//        for(int i=activity.getTimeWindows().size()-1; i >= 0; i--){
//            TimeWindow tw = activity.getTimeWindows().get(i);
//            if(tw.getStart() <= arrivalTime && tw.getEnd() >= arrivalTime){
//                return arrivalTime;
//            }
//            else if(arrivalTime > tw.getEnd()){
//                if(last != null) return last.getStart();
//                else return arrivalTime;
//            }
//            last = tw;
//        }
//        return Math.max(arrivalTime,last.getStart());
    }