ASP.NET Core Razor Add new data from Main page

Question

I am trying to add new data and on "Save" to automatically refresh data. However, on save I get error 

 

System.NullReferenceException: 'Object reference not set to an instance of an object.'

RoSafety.Pages.PTW.IsoC.IsoCertModel.ICData.get returned null.

 If I use a separate page for Post, the data is saved but on same page as OnGet is not. How should I do it?

  

[BindProperty]
        public ICContent ICContent { get; set; }
        public ICData ICData { get; set; }

        public async Task<IActionResult> OnGetAsync()
        {
            ICData = await _context.ICDatas
                .Include(a=>a.ICContents)
                .AsNoTracking()
                .FirstOrDefaultAsync(a => a.IdICD == 1);

            if (ICData == null)
            {
                return NotFound();
            }
            return Page();
        }

        public async Task<IActionResult> OnPostAsync()
        {
            if (!ModelState.IsValid)
            {
                return Page();
            }

            var emptyIsoCert = new ICContent();

            if (await TryUpdateModelAsync(emptyIsoCert, "ICContent",

                s => s.Equipment,
                s => s.EnergSource,
                s => s.IsoType,
                s => s.IsoMethod,
                s => s.LockNo,
                s => s.PreparedBy,
                s => s.ImplementedBy,
                s => s.VerifiedBy,
                s => s.IsoStatus ))

            {
                _context.ICContents.Add(emptyIsoCert);
                await _context.SaveChangesAsync();
                //return RedirectToPage("IsoCert");
                return await OnGetAsync();
            }

            return null;
        }