When binding a DataGrid to an ObservableCollection<T> with null items and replacing one such item with a non-null item a NullReferenceException is thrown. The culprit seems to be the PagedCollectionView.IsCurrentInSync property:
```
this.GetItemAt(this.CurrentPosition).Equals(this.CurrentItem)
```
should be
```
Object.Equals(this.GetItemAt(this.CurrentPosition), this.CurrentItem)
```
```
this.GetItemAt(this.CurrentPosition).Equals(this.CurrentItem)
```
should be
```
Object.Equals(this.GetItemAt(this.CurrentPosition), this.CurrentItem)
```