insert data via loop throws Failed to complete request: java.lang.NullPointerException in spring

Here I have a form that accepts package details and I have added dynamic form fields to get all the itineraries of that package. Please comment on what I must add to my question to make it more clear.

insert function

@PostMapping("/save-tour-package")
public String saveTourPackage(@ModelAttribute("tourPackage") TourPackage tourPackage, @RequestParam String[] day, @RequestParam String[] itinerary_title, @RequestParam String[] itinerary_description, @RequestParam String[] itinerary_altitude) {
    // save package to database
    TourPackage tour = tourPackageService.saveTourPackage(tourPackage);

    for (int i = 0; i < day.length; i++) {
        Itinerary ite = new Itinerary();
        ite.setPackages(tour);
        ite.setDay(day[i]);
        ite.setTitle(itinerary_title[i]);
        ite.setDescription(itinerary_description[i]);
        ite.setAltitude(itinerary_altitude[i]);
        itineraryRepo.save(ite);
    }
    return "redirect:/";
} 

save service implementation

@Override
public TourPackage saveTourPackage(TourPackage tourPackage) {
    return this.tourPackagesRepo.save(tourPackage);
}

view file

<div layout:fragment="content">
    <div class="container">
        <form th:action="@{/save-tour-package}" th:object="${tourPackage}" method="POST">
            <div class="form-group">
                <div class="form-group">
                    <label for="title">Title</label>
                    <input type="text" class="form-control" id="title" th:field="*{title}" placeholder="Title">
                </div>
                <div class="form-group">
                    <label for="description">Description</label>
                    <textarea class="form-control" id="description" th:field="*{description}"
                              placeholder="Description"></textarea>
                </div>
                <div class="row">
                    <div class="col-3">
                        <div class="form-group">
                            <label for="geography">Geography</label>
                            <input type="text" class="form-control" id="geography" th:field="*{geography}"
                                   placeholder="Geography">
                        </div>
                    </div>
                    <div class="col-3">
                        <div class="form-group">
                            <label for="location">Location</label>
                            <input type="text" class="form-control" id="location" th:field="*{location}"
                                   placeholder="Location">
                        </div>
                    </div>
                    <div class="col-3">
                        <div class="form-group">
                            <label for="difficulty">Difficulty</label>
                            <input type="text" class="form-control" id="difficulty" th:field="*{difficulty}"
                                   placeholder="Difficulty">
                        </div>
                    </div>
                    <div class="col-3">
                        <div class="form-group">
                            <label for="altitude">Altitude</label>
                            <input type="text" class="form-control" id="altitude" th:field="*{altitude}"
                                   placeholder="Altitude">
                        </div>
                    </div>
                    <div class="col-3">
                        <div class="form-group">
                            <label for="religion">Religion</label>
                            <input type="text" class="form-control" id="religion" th:field="*{religion}"
                                   placeholder="Title">
                        </div>
                    </div>
                    <div class="col-3">
                        <div class="form-group">
                            <label for="ethnic_people">Ethnic People</label>
                            <input type="text" class="form-control" id="ethnic_people" th:field="*{ethnic_people}"
                                   placeholder="Ethnic People">
                        </div>
                    </div>
                    <div class="col-3">
                        <div class="form-group">
                            <label for="accommodation">Accommodation</label>
                            <input type="text" class="form-control" id="accommodation" th:field="*{accommodation}"
                                   placeholder="Title">
                        </div>
                    </div>
                    <div class="col-3">
                        <div class="form-group">
                            <label for="transportation">Transportation</label>
                            <input type="text" class="form-control" id="transportation" th:field="*{transportation}"
                                   placeholder="Transportation">
                        </div>
                    </div>
                    <div class="col-3">
                        <div class="form-group">
                            <label for="minimum_pax">Minimum Pax</label>
                            <input type="text" class="form-control" id="minimum_pax" th:field="*{minimum_pax}"
                                   placeholder="Minimum Pax">
                        </div>
                    </div>
                    <div class="col-3">
                        <div class="form-group">
                            <label for="price">Price</label>
                            <input type="text" class="form-control" id="price" th:field="*{price}" placeholder="Price">
                        </div>
                    </div>
                </div>

                <div class="row">
                    <div class="col-2">Day</div>
                    <div class="col-3">Title</div>
                    <div class="col-3">Description</div>
                    <div class="col-3">Altitude</div>
                    <div class="col-1"></div>
                </div>
                <div class="row delete-field append-new-field">
                    <div class="col-2">
                        <input type="text" class="form-control" name="day">
                    </div>
                    <div class="col-3">
                        <input type="text" class="form-control" name="itinerary_title">
                    </div>
                    <div class="col-3">
                        <input type="text" class="form-control" name="itinerary_description">
                    </div>
                    <div class="col-3">
                        <input type="text" class="form-control" name="itinerary_altitude">
                    </div>
                    <div class="col-1">
                        <a href="javascript:;" class="text-danger delete-row"><i class="fas fa-minus-circle"></i></a>
                    </div>
                </div>

                <a href="javascript:;" onclick="addItineraryFields()" class="text-success">Add Fields</a>
                <div class="form-group">
                    <button type="submit" class="btn btn-info col-2"> Save Tour Package</button>
                </div>

            </div>
        </form>
    </div>
</div>

<div layout:fragment="after-script">
    <script>
        function addItineraryFields() {
            var html = '<div class="row delete-field"><div class="col-2">\n' +
                '                        <input type="text" class="form-control" name="day">\n' +
                '                    </div>\n' +
                '                    <div class="col-3">\n' +
                '                        <input type="text" class="form-control" name="itinerary_title">\n' +
                '                    </div>\n' +
                '                    <div class="col-3">\n' +
                '                        <input type="text" class="form-control" name="itinerary_description">\n' +
                '                    </div>\n' +
                '                    <div class="col-3">\n' +
                '                        <input type="text" class="form-control" name="itinerary_altitude">\n' +
                '                    </div>' +
                '                    <div class="col-1">\n' +
                '                        <a href="javascript:;" class="text-danger delete-row"><i class="fas fa-minus-circle"></i></a>\n' +
                '                    </div></div>';
            $('.append-new-field').append(html);
        }

        $(document).on('click', '.delete-row', function(e) {
            $(this).closest('.delete-field').remove();
            return false;
        });
    </script>
</div>