code: def MergeMessage(
        self, source, destination,
        replace_message_field=False, replace_repeated_field=False):
      
      tree = _FieldMaskTree(self)
      tree.MergeMessage(
          source, destination, replace_message_field, replace_repeated_field)
docs: Merges fields specified in FieldMask from source to destination.
  
      Args:
        source: Source message.
        destination: The destination message to be merged into.
        replace_message_field: Replace message field if True. Merge message
            field if False.
        replace_repeated_field: Replace repeated field if True. Append
            elements of repeated field if False.