ช่วยผมที!! Loading Related Entities ไม่ทำงานใน ASP.NET Core 2.1 (WebAPI)

    [Route("api/[controller]")]
    [ApiController]
    public class ItemsController : ControllerBase
    {
        private readonly SBSDbContext _context = new SBSDbContext();

        // GET: api/Items
        [HttpGet("getsbs_item")]
        public async Task<ActionResult<IEnumerable<SBS_ITEM>>> GetSBS_ITEM()
        {
            //return await _context.SBS_ITEM.ToListAsync(); // Nest เป็น Null

            return await _context.SBS_ITEM.Include("SBS_SALE_ORDER_DT")
                        .Where(x => x.ItemTypeCode == "FG"
                            && x.PicModelName != null
                            && x.PicModelPath != null
                            && x.ProductTypeCode == "JE")
                        .Select(y => new SBS_ITEM {
                            Code = y.Code,
                            BarCode = y.BarCode,
                            ItemTypeCode = y.ItemTypeCode,
                            ShortDesc1 = y.ShortDesc1,
                            ProductTypeCode = y.ProductTypeCode,
                            AlloyTypeCode = y.AlloyTypeCode,
                            PicModelPath = y.PicModelPath,
                            PicModelName = y.PicModelName,
                            SaleOrderDT = y.SaleOrderDT.Select(z => new SBS_SALE_ORDER_DT
                            {
                                Code = z.Code,
                                ProdCtrlCode = z.ProdCtrlCode,
                                ItemCode = z.ItemCode
                            })
                        }).ToListAsync();
        }