实体框架ASP Net MVC错误，当日期字段为空时，它将覆盖编辑操作期间的现有日期

我为CRUD项目创建了脚手架控制器，但存在一个错误。当我为MySql DB创建新的实体（记录）时，它可以按预期工作，其中一个值是HiredDate。但是，当我在其他视图中编辑“ FiredDate”之类的内容时，它将覆盖HiredDate的先前创建的记录，并将其设置为0001-01-01。

这是该模型的代码：

        [Column("City", TypeName = "varchar(100)")]
        public string City { get; set; }

        [Required]
        [Column("Department", TypeName = "varchar(100)")]
        public string Department { get; set; }

        [Required]
        [Column("HiredDate", TypeName = "date")]
        [Display(Name = "Hired On")]
        public DateTime HiredDate { get; set; }

        [Column("FiredDate", TypeName = "date")]
        [Display(Name = "Fired On")]
        public DateTime? FiredDate { get; set; }

        [Required]
        [Column("ModifiedDate", TypeName = "datetime")]
        [Display(Name = "Modified Date")]
        public DateTime ModifiedDate { get; set; }

和控制器代码进行编辑：

   public async Task<IActionResult> Edit(int id, [Bind("ID,FirstName,LastName,Email,Phone,Age,City,Department,FiredDate")] Employee employee)
        {
            if (id != employee.ID)
            {
                return NotFound();
            }

            if (ModelState.IsValid)
            {
                try
                {
                    _context.Update(employee);
                    await _context.SaveChangesAsync();
                }
                catch (DbUpdateConcurrencyException)
                {
                    if (!EmployeeExists(employee.ID))
                    {
                        return NotFound();
                    }
                    else
                    {
                        throw;
                    }
                }
                return RedirectToAction(nameof(Index));
            }
            return View(employee);
        }

和用于创建的控制器代码：

   public async Task<IActionResult> Create([Bind("FirstName,LastName,Email,Phone,Age,City,Department,HiredDate")] Employee employee)
        {
            if (ModelState.IsValid)
            {
                _context.Add(employee);
                await _context.SaveChangesAsync();
                return RedirectToAction(nameof(Index));
            }
            return View(employee);
        }

覆盖的结果如下所示：

我该如何解决？当我执行“编辑”操作并修改除HiredDate之外的任何其他字段时，我希望HiredDate保持不变（例如2020-01-01）。