docs: def _info_transformers(fields, transformers):
      """Utility function to determine transformer functions for variants
      fields."""
      if transformers is None:
          # no transformers specified by user
          transformers = dict()
      for f in fields:
          if f not in transformers:
              transformers[f] = config.DEFAULT_TRANSFORMER.get(f, None)
      return tuple(transformers[f] for f in fields)