docs: def _fit_invhashing_union(vec_union, docs):
      # type: (FeatureUnion, Any) -> FeatureUnion
      """ Fit InvertableHashingVectorizer on doc inside a FeatureUnion.
      """
      return FeatureUnion(
          [(name, invert_hashing_and_fit(v, docs))
           for name, v in vec_union.transformer_list],
          transformer_weights=vec_union.transformer_weights,
          n_jobs=vec_union.n_jobs)