An optional parameter must be a reference type

It is a couple days since I am trying to find what is the problem with my code. I need to create such dynamic links in my project: ParentCategory (Category) - ChildCategory (SubCategory) - Pages (Pages List) - PageDetails (page details by id).

I created ParentCategory and ChildCategory list successfully, both are dynamic, but when I press to go to Pages, this error appears:

The parameters dictionary contains a null entry for parameter 'Id' of non-nullable type 'System.Int32' for method 'System.Web.Mvc.ActionResult GetPages(Int32)' in 'bandymas.Controllers.PageController'. An optional parameter must be a reference type, a nullable type, or be declared as an optional parameter. Parameter name: parameters

My PageViewModels looks like this:

 public class Page
    {
        public int Id { get; set; }
        [Required]
        [Display(Name = "User name")]
        public string UserName { get; set; }
        [Required]
        [Display(Name = "ShortDescription")]
        public string ShortDescription { get; set; }
        [Required]
        [Display(Name = "Body")]
        public string Body { get; set; }
        [Required]
        [Display(Name = "Meta")]
        public string Meta { get; set; }
        [Required]
        [Display(Name = "UrlSeo")]
        public string UrlSeo { get; set; }
        [Required]
        [Display(Name = "User Image")]
        public string UserImage { get; set; }
        [Display(Name = "Experience")]
        public int Exp { get; set; }
        [Display(Name = "Logo")]
        public string Logo { get; set; }
        [Display(Name = "Website URL")]
        public string WebURL { get; set; }
        [Display(Name = "Facebook URL")]
        public string FacebookUrl { get; set; }
        [Display(Name = "Address")]
        public string Address { get; set; }
        public string Email { get; set; }
        public string PhoneNumber { get; set; }
        public string City { get; set; }
        public bool Published { get; set; }
        [DefaultValue(0)]
        public DateTime PostedOn { get; set; }
        public DateTime Modified { get; set; }
        public int ChildCategoryId { get; set; }



    }

    public class ParentCategory
    {

        public int Id { get; set; }
        [Required]
        [Display(Name = "Parent Category Name")]
        public string PCatName { get; set; }
        [Required]
        [Display(Name = "UrlSeo")]
        public string UrlSeo { get; set; }
        [Required]
        [Display(Name = "Description")]
        public string Description { get; set; }

        public ICollection<ChildCategory> ChildCategories { get; set; }
    }

    public class ChildCategory
    {

        public int Id { get; set; }
        [Required]
        [Display(Name = "Parent Category Name")]
        public string CCatName { get; set; }
        [Required]
        [Display(Name = "UrlSeo")]
        public string UrlSeo { get; set; }
        [Required]
        [Display(Name = "Description")]
        public string Description { get; set; }

        public int ParentCategoryId { get; set; }


        public ICollection<Page> Pages { get; set; }
    }

Here is my PageRepository

public IList<ParentCategory> GetParentCategories()
    {
        retu _context.ParentCategories.ToList();
    }

    public IList<ChildCategory> GetChildCategories(int Id)
    {
        retu _context.ChildCategories.Where(category => category.ParentCategoryId == Id).ToList();
    }

    public IList<Page> GetPages(int Id)

    {
        retu _context.Pages.Where(x => x.ChildCategoryId == Id).ToList();
    }

And PageController

public ActionResult Index()
    {
        var pcategories = _pageRepository.GetParentCategories();
        retu View(pcategories);
    }

    public ActionResult GetChildCategories(int ParentCategoryId)
    {
        var ccategories = _pageRepository.GetChildCategories(ParentCategoryId);
        retu View(ccategories);
    }

    public ActionResult GetPages(int Id)
    {

        var pages = _pageRepository.GetPages(Id);
        foreach (var page in pages)
        {


            page.ChildCategoryId = Id;
            page.UserName = page.UserName;
            page.City = page.UserImage;
            page.Address = page.City;
            page.PhoneNumber = page.Body;
        }
            retu View(pages);
    }

Here is GetChildCategories View

@using bandymas.Models
@using bandymas.Controllers

<div style="font-family:Arial">
@{
    ViewBag.Title = "GetChildCategories";
    Layout = "~/Views/Shared/_Layout.cshtml";
}

<h2>GetChildCategories</h2>
<h2>Child Categories List</h2>
<ul>
    @foreach (PageViewModels.ChildCategory ccategory in @Model)
    {
        <li>
           @Html.ActionLink(ccategory.CCatName, "GetPages", "Page",
new { ChildCategoryId = ccategory.Id }, null)
        </li>
    }
</ul>
</div>

And Here Is GetPagesView

@using bandymas.Models

@using bandymas.Controllers

@{
    ViewBag.Title = "GetPages";
    Layout = "~/Views/Shared/_Layout.cshtml";
}
@*@Html.BeginForm("GetPages", "Page",new { Id = Model.Id }, FormMethod.Get, null)*@
@foreach (var page in Model)
{



<div style="font-family:Arial">
    <h2>GetPages</h2>

    <h2>Pages List</h2>
    <ul>
        <li><input type="hidden" name="@page.Id" value="@page.Id" /></li>
        <li>
            @page.UserName
        </li>
        <li>
            @page.City
        </li>
        <li>
            @page.Address
        </li>
        <li>
            @page.PhoneNumber
        </li>
        <li>@Html.ActionLink("Back to ChildCategories List", "GetChildCategories", new { departmentId = @Model.DepartmentId })  </li>
    </ul>
</div>

}

This optional parameter error appears when I go to GetPages View from GetChildCategories View. I tried to change optional parameter in RouteConfig.cs and add int? next to Id,but it is still not working...