pipeline2dot fails with 'passthrough'

[sdpython]

data = pandas.DataFrame([
    dict(CAT1='a', CAT2='c', num1=0.5, num2=0.6, y=0),
    dict(CAT1='b', CAT2='d', num1=0.4, num2=0.8, y=1),
    dict(CAT1='a', CAT2='d', num1=0.5, num2=0.56, y=0),
    dict(CAT1='a', CAT2='d', num1=0.55, num2=0.56, y=1),
    dict(CAT1='a', CAT2='c', num1=0.35, num2=0.86, y=0),
    dict(CAT1='a', CAT2='c', num1=0.5, num2=0.68, y=1),
])

cat_cols = ['CAT1', 'CAT2']
train_data = data.drop('y', axis=1)


numeric_transformer = Pipeline(steps=[('scaler', StandardScaler())])
categorical_transformer = Pipeline([
    ('onehot', OneHotEncoder(sparse=False, handle_unknown='ignore'))])
preprocessor = ColumnTransformer(
    transformers=[
        ('cat', categorical_transformer, cat_cols)],
    remainder='passthrough')
pipe = Pipeline([('preprocess', preprocessor),
                 ('rf', RandomForestClassifier(n_estimators=2))])
pipe.fit(train_data, data['y'])