Не работает добавление даты в DataGrid. что делать?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Xml.Linq;

namespace ZooShop.Pages
{
///
/// Логика взаимодействия для AddTovariPage.xaml
///
public partial class AddTovariPage : Page
{
private readonly EquipmentRepairs _currentEquipmentRepairs = new EquipmentRepairs();
public AddTovariPage(EquipmentRepairs selectEquipmentRepairs)
{
InitializeComponent();
_currentEquipmentRepairs.Equipment = string.Empty;
_currentEquipmentRepairs.IssueType = string.Empty;
_currentEquipmentRepairs.IssueDescription = string.Empty;
_currentEquipmentRepairs.Status = string.Empty;
_currentEquipmentRepairs.AddedDate = null;

if (selectEquipmentRepairs != null)
{
DataContext = selectEquipmentRepairs;
_currentEquipmentRepairs.Equipment = selectEquipmentRepairs.Equipment;
_currentEquipmentRepairs.IssueType = selectEquipmentRepairs.IssueType;
_currentEquipmentRepairs.IssueDescription = selectEquipmentRepairs.IssueDescription;
_currentEquipmentRepairs.Status = selectEquipmentRepairs.Status;
_currentEquipmentRepairs.AddedDate = selectEquipmentRepairs.AddedDate;

}
else
{
DataContext = _currentEquipmentRepairs;
}

}

private void Add_Click(object sender, RoutedEventArgs e)
{
StringBuilder errors = new StringBuilder();

if (string.IsNullOrWhiteSpace(_currentEquipmentRepairs.Equipment))
errors.AppendLine("Укажите название обарудование");
if (string.IsNullOrWhiteSpace(_currentEquipmentRepairs.IssueType))
errors.AppendLine("укажите тип проблемы");
if (string.IsNullOrWhiteSpace(_currentEquipmentRepairs.IssueDescription))
errors.AppendLine("укажите описание");
if (string.IsNullOrWhiteSpace(_currentEquipmentRepairs.Client))
errors.AppendLine("укажите клиента");
if (string.IsNullOrWhiteSpace(_currentEquipmentRepairs.Status))
errors.AppendLine("укажите статус");
if (_currentEquipmentRepairs.AddedDate == null)
errors.AppendLine("укажите дату");

if (errors.Length > 0)
{
MessageBox.Show(errors.ToString());
return;
}

if (DataContext is EquipmentRepairs dataEquipmentRepairs)
{
if (dataEquipmentRepairs.RepairID == 0)
{
TechnoserviceEntities.GetContext.EquipmentRepairs.Add(dataEquipmentRepairs);
}

try
{
TechnoserviceEntities.GetContext.SaveChanges();
MessageBox.Show("Информация сохранена");
NavigationService.GoBack();
}
catch (Exception ex)
{
MessageBox.Show(ex.Message.ToString());
}
}
}

private void ComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{

}

private void Back_Click(object sender, RoutedEventArgs e)
{
NavigationService.GoBack();
}
}
}