The NullReferenceException is observed when the GridView is Grouped and rebound in the CellEditedEnded event handler.
Calling Rebind in CellEditEnded is not recommended since the elements are recreated and the cell does not have a parent at all at that time. If the grid is not grouped, the same approach (with calling Rebind) results in StackOverflow. This scenario puts the grid into an unstable state as it tries to recreate the elements and at the same time the rest of the operations on committing cell edit should be performed.