docs: def dump_is_last(self, obj):
          """Dump the boolean stating if the child in the relation is last.
  
          Dumps `None` for parent serialization.
          """
          if self._is_child(obj) and isinstance(obj, PIDNodeOrdered):
              if obj.children.count() > 0:
                  return obj.children.ordered('asc').all()[-1] == \
                      self.context['pid']
              elif obj.draft_child:
                  return obj.draft_child == self.context['pid']
              else:
                  return True
          else:
              return None