Datagrid current Row/Value

I am able to get out the Cell contents from WPF DataGrid with attached code. However, when I click anywhere in the UI, except the DataGrid, the following error comes out.

System.NullReferenceException was unhandled
  Message=Object reference not set to an instance of an object.
  Source=TestPlanningServiceReport
  StackTrace:
       at TestPlanningServiceReport.MainWindow.TestPlanningServiceReportDataGrid_CurrentCellChanged(Object sender, EventArgs e) in C:\DriveD\TESTS4WORK\TestPlanningServiceReport\MainWindow.xaml.cs:line 277
       at System.Windows.Controls.DataGrid.OnCurrentCellChanged(EventArgs e)
       at System.Windows.Controls.DataGrid.OnCurrentCellChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
       at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
       at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
       at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
       at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
       at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal)
       at System.Windows.DependencyObject.SetCurrentValueInternal(DependencyProperty dp, Object value)
       at System.Windows.Controls.DataGrid.set_CurrentCellContainer(DataGridCell value)
       at System.Windows.Controls.DataGrid.set_FocusedCell(DataGridCell value)
       at System.Windows.Controls.DataGridCell.OnAnyLostFocus(Object sender, RoutedEventArgs e)
       at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
       at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
       at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
       at System.Windows.UIElement.RaiseEvent(RoutedEventArgs e)
       at System.Windows.UIElement.OnLostFocus(RoutedEventArgs e)
       at System.Windows.UIElement.IsFocused_Changed(DependencyObject d, DependencyPropertyChangedEventArgs e)
       at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
       at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
       at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
       at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
       at System.Windows.DependencyObject.ClearValueCommon(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata)
       at System.Windows.DependencyObject.ClearValue(DependencyPropertyKey key)
       at System.Windows.Input.FocusManager.OnFocusedElementChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
       at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
       at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
       at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
       at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
       at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal)
       at System.Windows.Input.FocusManager.SetFocusedElement(DependencyObject element, IInputElement value)
       at System.Windows.Input.KeyboardNavigation.UpdateFocusedElement(DependencyObject focusTarget)
       at System.Windows.FrameworkElement.OnGotKeyboardFocus(Object sender, KeyboardFocusChangedEventArgs e)
       at System.Windows.Input.KeyboardFocusChangedEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
       at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
       at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
       at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
       at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
       at System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
       at System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted)
       at System.Windows.Input.InputManager.ProcessStagingArea()
       at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
       at System.Windows.Input.KeyboardDevice.ChangeFocus(DependencyObject focus, Int32 timestamp)
       at System.Windows.Input.KeyboardDevice.TryChangeFocus(DependencyObject newFocus, IKeyboardInputProvider keyboardInputProvider, Boolean askOld, Boolean askNew, Boolean forceToNullIfFailed)
       at System.Windows.Input.KeyboardDevice.Focus(DependencyObject focus, Boolean askOld, Boolean askNew, Boolean forceToNullIfFailed)
       at System.Windows.Input.KeyboardDevice.Focus(IInputElement element)
       at System.Windows.UIElement.Focus()
       at System.Windows.Documents.TextEditorMouse.MoveFocusToUiScope(TextEditor This)
       at System.Windows.Documents.TextEditorMouse.OnMouseDown(Object sender, MouseButtonEventArgs e)
       at System.Windows.Controls.Primitives.TextBoxBase.OnMouseDown(MouseButtonEventArgs e)
       at System.Windows.UIElement.OnMouseDownThunk(Object sender, MouseButtonEventArgs e)
       at System.Windows.Input.MouseButtonEventArgs.InvokeEventHandler(Delegate genericHandler, Object genericTarget)
       at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
       at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
       at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
       at System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
       at System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
       at System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted)
       at System.Windows.Input.InputManager.ProcessStagingArea()
       at System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
       at System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
       at System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel)
       at System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
       at System.Windows.Interop.HwndSource.InputFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
       at MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
       at MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
       at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
       at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)
       at System.Windows.Threading.Dispatcher.InvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
       at MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
       at MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
       at System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
       at System.Windows.Threading.Dispatcher.PushFrame(DispatcherFrame frame)
       at System.Windows.Application.RunDispatcher(Object ignore)
       at System.Windows.Application.RunInternal(Window window)
       at System.Windows.Application.Run(Window window)
       at System.Windows.Application.Run()
       at TestPlanningServiceReport.App.Main() in C:\DriveD\TESTS4WORK\TestPlanningServiceReport\obj\x86\Debug\App.g.cs:line 0
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: