code: def save(self) -> None:
          
          if self._output_dir is None:
              raise ValueError('Can not save TrainingTrace without output dir.')
          yaml_to_file(self._trace, self._output_dir, CXF_TRACE_FILE)
docs: Save the training trace to :py:attr:`CXF_TRACE_FILE` file under the specified directory.
  
          :raise ValueError: if no output directory was specified