def encode_value(self, string_list, values):
    """Encode the value of this feature into the CSV line."""
    if self._encoder:
      string_list[self._index] = self._encoder.encode_record(values)
    else:
      string_list[self._index] = _to_string(values[0]) if values else ''
Encode the value of this feature into the CSV line.
tensorflow_transform/coders/csv_coder.py