docs: def get_batch_method(self):
          """
          Returns a change batch for SharePoint's UpdateListItems operation.
          """
          if not self._changed:
              return None
  
          batch_method = E.Method(Cmd='Update' if self.id else 'New')
          batch_method.append(E.Field(text_type(self.id) if self.id else 'New',
                                      Name='ID'))
          for field in self.fields.values():
              if field.name in self._changed:
                  value = field.unparse(self._data[field.name] or '')
                  batch_method.append(E.Field(value, Name=field.name))
          return batch_method