code: def save_to_file(self, data_group):
      if type(self.output_data) is not list:
          for file_idx, output_filename in enumerate(
              self.output_filenames
          ):
              if self.overwrite or not os.path.exists(output_filename):
                  save_data(
                      np.squeeze(self.output_data[..., file_idx]),
                      output_filename,
                      reference_data=data_group.preprocessed_affine,
                  )
  
      return
  
imports: import os
  import numpy
  from deepneuro.utilities.util import add_parameter, replace_suffix, cli_sanitize, docker_print
  from deepneuro.utilities.conversion import read_image_files, save_data
label_desc: Use image node_id 9 for calling the Preprocessor obj's underlying member method code with example usage: obj.save_to_file(data_group) without return types