code: def append_account_merge_op(self, destination, source=None):
          
          op = operation.AccountMerge(destination, source)
          return self.append_op(op)
docs: Append a :class:`AccountMerge
          <stellar_base.operation.AccountMerge>` operation to the list of
          operations.
  
          :param str destination: The ID of the offer. 0 for new offer. Set to
              existing offer ID to update or delete.
          :param str source: The source address that is being merged into the
              destination account.
          :return: This builder instance.