The value '' is invalid

@page
@model MealApp.Pages.Meals.AddModel
@{
    <h1>Dodaj posiłek</h1>

    <form method="post" class="mt-3">
        <input type="hidden" asp-for="Meal.Id" />
        <div class="form-group row">
            <label asp-for="Meal.MealName" class="col-sm-2 col-form-label">
            </label>
            <div class="col-sm-10">
                <input asp-for="Meal.MealName" class="form-control" placeholder="Nazwa posiłku">
            </div>
        </div>
        <div class="form-group row">
            <label asp-for="Meal.Type" class="col-sm-2 col-form-label">
            </label>
            <div class="col-sm-10">
                @Html.DropDownListFor(p => p.Meal.Type.Id, new SelectList(Model.Types, "Id", "TypeName"), "--Wybierz typ posiłku--", new { @class = "form-control" })
            </div>
        </div>
        <div class="form-group row">
            <label asp-for="Meal.Description" class="col-sm-2 col-form-label">
            </label>
            <div class="col-sm-10">
                <input asp-for="Meal.Description" class="form-control" placeholder="Opis">
            </div>
        </div>
        <div id="myTable" class="datatable" data-hover="true" data-border-color="dark ">
            <table class="table datatable-table">
                <thead class="datatable-header">
                    <tr>
                        <th>Produkt</th>
                        <th>Ilość</th>
                    </tr>
                </thead>
                <tbody class="datatable-body">
                    <tr>
                        <td>
                            @Html.DropDownListFor(p => p.Meal.MealProducts[0].ProductId, new SelectList(Model.Products, "Id", "ProductName"), "--Wybierz produkt--", new { @class = "form-control" })
                        </td>
                        <td>
                            <input asp-for="Meal.MealProducts[0].Quantity" class="form-control" placeholder="Ilość" />
                        </td>
                    </tr>
                </tbody>
            </table>
        </div>
        <button type="button" id="add-row" class="btn btn-primary">Dodaj produkt</button>
        <div class="form-group row">
            <div class="col-sm-10">
                <button type="submit" class="btn btn-primary">Dodaj</button>
                <a asp-page="/Products/Index" class="btn btn-danger">Cancel</a>
            </div>
        </div>
    </form>
}

public class Meal
    {
        public int Id { get; set; }
        public TypeOfMeal Type { get; set; }
        public string MealName { get; set; }
        public string Description { get; set; }
        public List<MealProduct> MealProducts { get; set; }
    }

<input type="hidden" data-val="true" data-val-required="The Id field is required." id="Meal_Id" name="Meal.Id" value="">

    public class AddModel : PageModel
    {
        private readonly IMealRepository mealRepository;
        private readonly IProductRepository productRepository;
        private readonly ITypeOfMealRepository typeOfMealRepository;

        public Meal Meal { get; set; }
        public IEnumerable<Product> Products { get; set; }
        public IEnumerable<TypeOfMeal> Types { get; set; }
        public AddModel(IMealRepository mealRepository,
            IProductRepository productRepository,
            ITypeOfMealRepository typeOfMealRepository)
        {
            this.mealRepository = mealRepository;
            this.productRepository = productRepository;
            this.typeOfMealRepository = typeOfMealRepository;
        }
        public IActionResult OnGet()
        {
            Types = typeOfMealRepository.GetAllTypes();
            Products = productRepository.GetAllProducts();
            return Page();
        }
        public IActionResult OnPost(Meal meal)
        {
            Meal = meal;
            if (ModelState.IsValid)
            {
                mealRepository.AddMeal(Meal);
                return RedirectToPage("Index");
            }
            else
            {
                return RedirectToPage("Error");
            }
        }
    }