code: def load_existing_json():
          
          dir = logger.get_logger_dir()
          fname = os.path.join(dir, JSONWriter.FILENAME)
          if tf.gfile.Exists(fname):
              with open(fname) as f:
                  stats = json.load(f)
                  assert isinstance(stats, list), type(stats)
                  return stats
          return None
docs: Look for an existing json under :meth:`logger.get_logger_dir()` named "stats.json",
          and return the loaded list of statistics if found. Returns None otherwise.