Plotly Dash:如何解决错误dash_html_components.Div检测到道具的组件不是子组件

import dash
import dash_core_components as dcc
import dash_html_components as html

app = dash.Dash()

app.layout = html.Div(
    children=[
        dcc.Graph(
            id='example-graph',
            figure={
                'data': [
                    {'x': [1, 2, 3], 'y': [4, 1, 2], 'type': 'bar', 'name': 'SF'},
                    {'x': [1, 2, 3], 'y': [2, 4, 5], 'type': 'bar', 'name': u'Montréal'},
                ],
                'layout': {
                    'title': 'Dash Data Visualization'
                }
            }
        )
    ]
)

if __name__ == '__main__':
    app.run_server(debug=True)

import dash
import dash_html_components as html

app = dash.Dash()

app.layout = html.Div(
    children=[
        html.H1('Hello Dash'),
        html.P('Dash: A web application framework for Python.')
    ]
)

if __name__ == '__main__':
    app.run_server(debug=True)