"mes":"Value cannot be null. (Parameter 'source')" when want to show value which is true in view with checkbox

Question

Hi I have 3 tables: Role , Permission , RolePermission In my Razor page view I want to show each permission that is true for a special role with marking the check box . In every role I show all permission in a tree model (my permission is a parent child table) So for this reason I make a model

           [Table("tblPermission", Schema = "cmn")]
            public class Permission
            {
          [Key]
             public int PermissionId { get; set; }
             public string PermissionTitle { get; set; }
            public int? ParentId { get; set; }

           [ForeignKey("ParentId")]
           public List<Permission> Permissions { get; set; }
           public List<RolePermission> RolePermissions { get; set; }
           }

And two action

  [BindProperty]
    public Role Role { get; set; }
    public void OnGet(int id)
    {
        Role = _permissionService.GetRoleById(id);
       var b= _permissionService.GetAllPermission();
        ViewData["Permissions"] = b;
       
        var a= _permissionService.permissionsRole(id);
        ViewData["SelectedPermission"] = a;
    }


    public IActionResult OnPost()
    {
        if (!ModelState.IsValid)
        {
            return Page();
        }
        _permissionService.UpdateRole(Role);
        return RedirectToPage("Index");
    }

And my view is like bellow :

 @page "{id}"
 @using Entities.Permission
 @model Pages.Admin.Roles.EditRoleModel
 @{
   ViewData["Title"] = "Edit role";
   List<Permission> permissions = ViewData["Permissions"] as List<Permission>;
   List<int> SelectedPermissions = ViewData["SelectedPermissions"] as List<int>;
  }

<div class="panel-body">
   <ul>
     @foreach (var permission in permissions.Where(p => p.ParentId == null))
       {
      <li>
      <input type="checkbox" name="SelectedPermission" 
@((SelectedPermissions.Any(p=>p==permission.PermissionId)?"checked":"")) 
value="@permission.PermissionId" /> @permission.PermissionTitle
 @if (permissions.Any(p => p.ParentId == permission.ParentId))
{
<ul>
@foreach (var sub in permissions.Where(p => p.ParentId == permission.PermissionId))
  {
    <li>
  <input type="checkbox"  name="SelectedPermission"  
 @((SelectedPermissions.Any(p=>p==sub.PermissionId)?"checked":"")) value="@sub.PermissionId" 
/> @sub.PermissionTitle
</li>
  }   
 </ul>
  }
 </li>
  }
</ul>
</div>

At this line “@((SelectedPermissions.Any(p=>p==sub.PermissionId)?"checked":""))” I get the error : "mes":"Value cannot be null. (Parameter 'source')" .And when I Check out I found that none of my viewData is not null.