code: def FoldByteStream(self, mapped_value, context=None, **unused_kwargs):
      
      elements_data_size = self._CalculateElementsDataSize(context)
      if elements_data_size is not None:
        if elements_data_size != len(mapped_value):
          raise errors.FoldingError(
              'Mismatch between elements data size and mapped value size')
  
      elif not self._HasElementsTerminator():
        raise errors.FoldingError('Unable to determine elements data size')
  
      else:
        elements_terminator = self._data_type_definition.elements_terminator
        elements_terminator_size = len(elements_terminator)
        if mapped_value[-elements_terminator_size:] != elements_terminator:
          mapped_value = b''.join([mapped_value, elements_terminator])
  
      return mapped_value
docs: Folds the data type into a byte stream.
  
      Args:
        mapped_value (object): mapped value.
        context (Optional[DataTypeMapContext]): data type map context.
  
      Returns:
        bytes: byte stream.
  
      Raises:
        FoldingError: if the data type definition cannot be folded into
            the byte stream.