'Sets the staff lock on the chapter, sequential, and vertical
If the corresponding argument is False, then the field is deleted from the xblock'

def _update_staff_locks(self, chapter_locked, sequential_locked, vertical_locked):

    self.chapter = self._set_staff_lock(self.chapter, chapter_locked)
    self.sequential = self._set_staff_lock(self.sequential, sequential_locked)
    self.vertical = self._set_staff_lock(self.vertical, vertical_locked)
